You asked for cheap and real. Well, it's only 88% real, but it's the cheapest possible source aside from catching squirrels. It does require some labor. You could make it once a week.
Lentils + rice protein powder!
1 lb bag of lentils provides 98 g protein
at $0.006/g.
Nutribiotic rice protein powder costs about $0.027/g at the cheapest sites.
MLO rice protein powder is about $0.020/g
[there is one other source, pretty cheap and reputedly high quality, but I am not sure if I am allowed to post a link, so pm me if you want it]
You would add 1 part Nutribiotic to 8 parts lentils, or 1.25 part MLO to 8 parts lentils
to get a complete protein. You would do even better if you sprouted your lentils before you cooked them.
This works out to about $0.0083/g protein for lentils + Nutribiotic and $0.0079/g protein for lentils + MLO.
Compare this to (for my area, yours might be different)
cost per gram of protein
mackerel, canned $0.011 (Sav-a-lot, this is what I feed my dogs)
light tuna canned $0.020 ($0.50 for a 6 oz can, drained)
whole eggs $0.018 ($1.85 for 18)
whey powder $0.017 to $0.054 and up
nonfat milk $0.023 (about $3/gallon)
nonfat cottage cheese $0.024 (about $2 for the container)
eggs. whites only $0.026
mori nu silken tofu xtra lite $0.041
I am not sure where Costco chicken fits into this. Probably somewhere between t he egg whites and the tofu.
You could use any other bean (except for soy, which doesn't need any addition, like most other beans do),but they are all more expensive than lentils. The dried cooked bean + rice protein combo will still be cheaper than virtually anything else you can buy unless you are buying super gourmet rare varieties of beans like the kind they sell at Dean and Deluca.