When you look at seed prices, don't just look at the price per packet. You need to look at the weight of the seeds. Cheaper seeds usually have fewer seeds. If you buy larger quantities from the seed companies it gets a lot cheaper.
You will have a better selection of cultivars from a seed company so you will have more choices. Are they better? It often depends on where you live. Some cultivars will do better in short season, colder climates and others do better in the heat. Newer varieties cost more than older ones in general. At Walmart you will get Beefsteak tomatoes, but there are a lot of different beefsteak type tomatoes and there are a lot of different Brandywine strains so you really don't know which one you are getting. Walmart and the box stores buy their seeds in bulk and for stores all over the country. You have to be aware that in some places the seeds, bulbs and plants, that are in the stores may not be appropriate for where you live because they are not going to do well in your zone. That is where you have to do your homework first.
What you find in the stores will usually be older more established varieties and they do well in most parts of the country or are the most popular.
As for germination rates a lot depends on the variety. Some things like stevia and rosemary have poor germination rates to start with and some seeds require stratification to germinate well. Germination can also be affected by how the seeds are stored. Most stores replace their seeds every year and get new ones, but store managers decide where the products are placed. I prefer to buy my seeds when the racks are inside the air conditioned store and not if they are outside in the greenhouse exposed to heat and light during the day; 20+ degrees of variance in temperature in a 24 hour period, and exposed to moisture when they water the plants. I find even the cheap seeds germinate well if they are fresh, have been properly stored, and they are a variety with good germination. Usually seed companies try to put enough seed in a packet to get at least 80% germination under ideal conditions. Some seeds are just more expensive than others and their germination rate is poor, but the seed packet will usually warn you about that. Really difficult seeds are usually in a foil pouch inside the seed packet. Park seed is expensive but they do package all their seed in a foil pouch to preserve them longer.
There are seed companies like Ferry Morse that sell to the general public small packets of seed usually enough for a 20 ft row. The seeds online or in the stores are fairly inexpensive and the quality has been fine. They even give more seeds than other companies (for the same variety) that are more expensive. They don't spend a lot of money on packaging. Their selection though is limited.
Some companies specialize in certain types of seed, spend more on packaging or are certified organic and non gmo and you do pay more for those seeds. Some companies are better than others in customer service and quality for the price you pay. Some companies specialize in certain types of seed so they give you a little more information and a lot more choices or have difficult to find seeds, and that makes it worthwhile. If you buy seeds from another country expect to pay more for the shipping and international fees. You also have to look at the shipping and handling fees and for those of us who do not live in the contiguous states, there are a lot of companies that will not ship certain items to us at all. There are also quarantines set up by state departments of ag restricting import of certain seeds and plants. Right now there is a crucifer seed restriction in Washington state where they are trying to control a seed borne fungus. Hawaii can get rape seeds but cannot send any to the mainland US. A lot of things cannot be shipped in or out of Hawaii. Plants and seeds have to be taken down to the plant quarantine station and inspected and packaged in their presence before they will stamp it to be mailed out, then you have to go to the post office next door and stand in that line to mail it.
I can get bareroot roses shipped in but not bulbs or rhizomes from most places. I get charged to wash the soil from the bareroot roses (Huh???), but the roses are shipped when they are ready to plant. Here that is around or on Christmas Day. The roses from the catalog will have longer roots that have not been chopped or compressed to fit in the packaging. They usually send grade 1 roses. The roses at walmart are usually grade 1 1/2. While the Walmart roses are a lot cheaper, you have to get them soon after the store receives them, because the store manager decides where to put them and it is often not in the best place like outside in the sun. You want to get dormant roots and not plants that have already broken dormancy for the best survival rates. The canes on the Walmart plants are usually smaller and there can be some damage so you have to look closely. They take a little longer to get established but the ones that survive do fairly well. The catalog usually will replace roses that fail to grow.
When you get seeds, look for the country of origin. If the climate is very different from yours, the seed may not do as well.
Seed companies do have sales, usually if they are overstocked or they are discontinuing an item. If you have problems with your order or you get sent the wrong seeds, the reputable companies will replace them. Burpee sent me the wrong seeds and enough people complained so they sent new seeds and a letter to everyone who ordered the seeds from them. Jackson and Perkins forgot to send my roses, so I called them. They sent my roses out within 2 days and an amaryllis as an apology. By the time you find out the packet from Walmart was not the yellow tomato you were expecting the seed packet and receipt are long gone.
Besides it is just fun to look through those catalogs. Catalog descriptions usually tell you about the seeds good points but you have to hunt for the bad ones. They tell you if the seeds have good disease resistance but not always if they don't. Tomatoes that don't describe the flavor and the description talks mostly about its great disease resistance.
If you are new at gardening it is a good idea to look up the plants on your local extension site. It will tell you how and when to plant and what varieties do well (although they may not taste the best). If certain diseases are an issue in your area, you want to get seeds that have some resistance or you will have to do some advance planning like if you have nematodes you need to have nematode resistance or plant in pots off the ground in sterile potting mix and be careful to wash tools and hands before using them in the pots. If you live in a humid area, and you have a plant that does not have fungal resistance, plan on needing a regular preventive fungicide program especially in humid conditions. If you live in a hot area where summer temps exceed 90 degrees, you need to have heat resistant tomatoes. Northern gardeners have to plant short season varieties. Southern gardeners with longer growing seasons can plant early, mid season and long season varieties.
My favorite seed companies are
TGN pumpkin nook (inexpensive but quality seeds, limited choices)
Harris seeds ( bulk seeds)
Kitazawa seed - Asian seeds suitable for Hawaii
Evergreen seeds- Asian seeds
Thompson and Morgan - They are located in UK so international shipping and charges apply so I have to have a big enough order but their seeds are packaged well and are very good.
Stokes seed - bulk seed to US and Canada
Tomato Growers Supply - a very good selection of tomatoes, peppers, and some eggplant
Pepper Gal - small business in Florida. Website does have some design issues, but I am used to it. Simple packaging in a small manilla packet. I think it is a home business.
Pepper Joe's - very good for hard to find seeds.
Dixondale farms - onion, garlic, bulbs and growing information and one of the few places that does ship to Hawaii for an additional charge.
High Mowing seeds- organic seeds limited choices but good bulk prices.