Actually, I read somewhere that you really do not save that much growing your own food. Food is something we all need but are reluctant to pay a premium for, so unless you are buying organic or a gourmet item, the markup on staple groceries is only a few pennies.
Add to that, the average homeowner buys seeds, garden supplies, tools, compost, amendments, fertilizers, and muscle cream from their local Walmart or hardware store instead of buying in bulk or getting a discount (requires and account) from an agricultural supplier so they do pay more.
You have though hit on some of the main reasons we do grow our own food
1. Fresh picked herbs and vegetables cannot be beat for flavor and freshness.
2.You know what went into to your garden so you know whether or not it was grown organically and how the pests and diseases were controlled.
3. There is a sense of satisfaction and accomplishment from actually being able to harvest and enjoy something you have spent so much effort in producing.
4. You did earn some health benefits from being active. While my doctor doesn't consider anything that is not aerobic 'exercise', I doubt he has every tried to double dig a garden bed.
5. If you grow a lot of vegetables you can share them with your friends and neighbors until even they don't want anymore, then you can take it down to your local food bank that takes perishables where they are always appreciated or some people do grow extras to sell at their local farmer's market so they can pay for more seeds and supplies for next years' garden.
Happy gardening in Hawaii. Gardens are where people grow.