Thanks for the tips.
As if you couldn't guess, Walmart was consistently the least expensive. Walmart's "great value" brand was especially inexpensive, it was 10-35% less expensive than the off brands at the other stores, but even comparing popular brands like "Del Monte" they were still less expensive by a margin.
Beware of "value brands" and the like. Many times these products are inferior in quality. You get what you pay for. I am by no means an experienced sailor but I would think that if you are going to be out at sea for an extended period of time, you would want quality nutrition.