By “undercut” do you mean these communities would sell their own produce? Local farmers can sell to decent grocery stores and co-ops.

But either way: massive gardens would require massive amounts of labor. If you wish to reduce labor, you need machinery, which is expensive, and organized fields, which requires some management and oversight. And crop management. And so on. I don’t think any small-scale farm can “undercut” a massive conglomerate that produces enough potatoes a year to fill Ohio three layers deep. (Exagerrating of course, but you get the idea)