At GFS, I can get a 5-pound bag of boneless/skinless chicken breasts for $9.99, sometimes $7.99 if they are one sale, but that is rare. That's only $2.00 per pound. The quality varies a lot. Sometimes the chicken is almost all meat, sometimes a LOT of fat, sometimes a lot of bloody areas. Once you trim off the junk, the amount of chicken left can vary quite a bit.
I've actually done the nothing but oatmeal thing last year when I was working overseas. In my case it was nothing but oatmeal 1-2 times per day for 2-months. Got really skinny and weak. Given the option I'd prefer not to go that route. But, if I could get some really cheap protein powder, then I may try that.
With chicken, veg, EVOO, I could possibly do 1-2 meals a day. I would have to cut my protein down to about 100-grams per day or less.
The oatmeal suggestion is currently looking good...