It varies greatly, I used to be far more picky about what I ate when I started, right now I settle for convenience... in doing so, both my costs and preparation time have improved... I am down to 14 chicken breasts/week, 7 cans of tuna/week, 2 salmon steaks/week... a shitload of oats, lots of water, lbs/whey per month... that is pretty much about it... the rest is some potatoes here and there, multivitamins and Vitamin C...
You do the math, is not much, maybe about 200-300 $/month