Sometimes it is hard to put a price on intangibles. I harvested corn about 20 ears (I only had 39 plants and the storms knocked a few down). At my prices 75 cents each, it would have been about $15 and it took half my garden space, so opportunity cost. But, the corn I grew was sweeter than what is sold in the market and there is the satisfaction of growing it.
Chayote sells for $1.69 a pound and I can't use it all. It takes no effort to grow it since it lives on rain and neglect
Meyer lemons and Bearrs lime they sell for almost a dollar for the lemons and three for a dollar for the limes. The Meyer will fruit 2-3 times a year and the Bearrs, I get from my moms house (I raid her tree, so does her neighbor). I get over 50 lemons from a 3 foot tree, hundreds of calamondin ( retails for $1.69 a pound), and over 50 limes from my mothers tree. I'm guessing if I had to buy all of that it might come close to $100
Hot peppers sell for $7-$12 a pound. I probably harvest about $30 worth, the rest the birds get. Jalapeno's are cheap at $3 a pound but they aren't very hot so I don't grow as much. They are heavier so maybe $5-$6 retail
Herbs at $3 a bunch, I save a lot. I use bay leaf, curry leaf, lemon grass, green onions, chives, thyme, basil, cilantro, Italian parsley, cutting celery, cholesterol spinach, Jamaican oregano, marjorram, culantro, ginger, turmeric, and roselle. I probably save about $75 a year on that.
Vegetables I do grow but, since I don't time them well and most are highly perishable, I probably am running negative. I cannot eat all of the lettuce or Chinese cabbage I grow. I do give away daikon, eggplant, peppers, and eat most of the beets, spinach and araimo. I do save about $30 a month because when I don't have vegetables or herbs, I have to buy them.
I can't say I come out ahead pocket wise since this year I spent
$139 on mail order seeds and about another $30 for other seeds locally.
Water costs - $100 a month.
Slug bait $58 for 20 lbs. I have probably spent over $100 this year alone on slug control
Replacement tools (broken or lost) $200
Fertilizer and pest control- $200-$300 over the course of the year
Compost / Peat moss/ Perlite/Cinders - Peat moss $18-$24 per 3.8 cu ft, Compost $14-$16 per 2-3 cu ft, MG potting soil $17 per 2 cubic ft, Cinder $5.50 3/4 cu ft. Perlite $32 for 4 cu ft bag.
Like most people I am probably working for less than the minimum wage in the garden, but if you are doing something you enjoy doing, it really isn't work, even if it really hurts at the end of the day (Masseuse $75 an hour).
In the long run I probably don't save a lot of money growing my own food since the costs are also very high. I can spend almost $200 a month on garden related things like seeds, fertilizer, amendments and sprinkler parts and I know I don't spend that much on produce ( I buy bananas, onions, garlic, and other fruits). I probably do save $100 a month on produce I grow that I don't have to buy like the citrus, eggplant, peppers, tomatoes, chard cucumbers, and herbs which I use a lot. I don't save as much on things I grow too much of like beans, lettuce, Kai choy cabbage or things that are perishible; have a short window to harvest and do not cut and come again and have to be replanted often like spinach, greens and beets. These things I still haven't figured out the optimal amount or remember to plant on time for succession. It has an opportunity cost as well since unlike James, I don't have a lot of land so anything ends up compost is a lost opportunity to grow something else.
Still what I grow tastes so much better than what is in the market that it is worth it. Except for some of the tomatoes I tried, some are great but others are just so-so. I can never really get a cucumber, pepper, bean, snowpea, or herb as good or crisp as the ones I grow myself.
Happy gardening in Hawaii. Gardens are where people grow.