It may be different now with the skyrocketing costs of food at the market, but I figured out and also read somewhere that if you take into account your inputs: land, water, fertilizer, amendments (compost, manure, peat moss, sand, vermiculite, perlite, coir, topsoil, etc), seeds, plants, seed starting supplies and set up, electricity, garden equipment and tools, time weeding, pest and disease control, waste disposal, etc and your time and opportunity cost if you chose to go skiiing instead, or use the land or room for something else, then you really don't save that much money growing your own. Unless, like James you have a lot of land; have established what grows best and efficiently; a clientelle and market to grow and sell large quantities of produce, you may just manage to break even.
Especially, when starting out, you may actually spend more than you would if you buy the produce, because you have start up costs for building the garden; seeds and plants; figuring out what grows well; amending the soil which might mean getting a soil test to see what you have; tools (tools can last for years but in year 1, you might have to buy a lot. Where tools are concerned it pays to buy quality so it does the job and lasts for years); seed starting set up racks, lights, grow trays, soil or blocks for soil trays; and a lot more hours just putting it all together. When you start out you may also not know where to get the best seeds, or where the agricultural suppliers are. If you buy in large enough quantities, you can get an account and save up to 20%. Most home gardeners are paying retail at the big box stores, and that is fine for small start up gardens and containers but it is also what raises production costs. The price of seeds now has more than doubled, so I am glad that I can save some of my seeds and for seed exchanges on the forum and with my circle of friends.
The reward for preserverence though is the feeling of accomplishment and really enjoying the fruits of your labors and knowing what really fresh produce is supposed to taste like. No more limp cucumbers, wilted greens, if you are lucky you will find a great tomato, but if not, you know there has to be one out there that is better than what is available in the market.
It is great to share your bounty with friends and family, although I admit, there can be too many chayote. Making friends with other gardeners who can share their experience; seeds; produce; and fellowship.
Happy gardening in Hawaii. Gardens are where people grow.