Only slightly related. One weird thing I noticed when moving to Japan is that peanuts and beans were way more expensive than the US. I guess the equivalent here would be moyashi (bean sprouts) and cabbage.
soy (in the form of edamame, tofu, and natto) is probably the cheapest option. Eggs are usually next on the list for people over here.
Edit: seafood might or might not be an option before eggs depending upon where one lives. Organ meat as well as we eat heart, liver, etc. a lot here as well.