Compost is a home project (and available in some cities as part of the waste management system) and nutritious for plants; but most of the things I grow as food I don't fertilize much or any. The fruit trees once a year or so, the garden soil sometimes in between planting or when growing watermelon or squash, bigger things do need some extra fertilizer (and tomatoes like some) but most seem to do fine with good soil and crop rotation/companion planting. Farmers have to use more because they've depleted the soil with monoculture. I still don't think it's cost effective when time is factored in, but it's better fresher food and not as fussy as farming.

Industrial farming, as commonly practiced, is unsustainable. We basically just turn fossil fuels into food, and degrade our environment (including our food production capacity) while doing it.

Vegetable gardening can definitely save you money, including negations. Most people, including myself, just do it as a hobby though.

I started vegetable gardening last year, and all my inputs, so far, have been free (with the exception of seeds, seed starting soil, and various inexpensive tools). I've used chicken manure from Craigslist (had to shovel it myself), home made compost (grass/weed clippings, arborist wood chips, kitchen scraps), and sometimes urine for extra nitrogen (lol). I've noticed that with adding compost on top of my soil, I don't really need much, if any, fertilizer (manure or urine).

Nitrogen-fixing plants can also be used to bring more nitrogen into your little garden ecosystem.

I haven't used any pesticides or herbicides. I just hand pull any weeds when I see them and mulch with either wood chips or paper with compost on top. I hand-pick caterpillars when I see them (or hunt for them when I see a lot of damage), and just throw them into my lawn (they don't seem to be able to make it back).

I'm still learning and experimenting, and have had certain species decimated by pests (brassicas), but I think I can experiment with timing, varieties, and hope natural predators will move in (I started planting plants in my perrenial beds that are supposed to attract beneficial insects, and put a birdhouse near my garden). If I find I can't grow certain crops or varieties well in my environment, I just won't. I save the seeds from my healthiest plants, so hopefully, this will eventually select for varieties that do well in my particular conditions.

Efficiency in produce per monetary cost. But for efficiency of human health per natural resources, I think gardening might be a winner.