Maybe chicken livers. They are very cheap and the feed commercial chickens are raised on 100% protein (I live in the chicken capitol of the world. Commercial chicken farming is common knowledge here) Nothing go to waste from a commercial chicken. Not even the poo. b/c the poo is still like 90% protein (they use the poo for fertalizer and commercial cattle feed).
Anyway, that means lot of protein in their livers too.
a rat i saw some in petco yesterday and thought their freezer was infested. then i stood behind a shelf and watched some old lady screem when she opened it to get frozen food.
do not do chicken!!!!!!!!!!!! beef heart rarely, at that age do frozen blood worms, flake foods, lettuce if they will, and when they get a bit bigger do mostly SHRIMP!!! Trust me on this one unless you konw someone else with a 11" red lol.
I agree with viral mouser
although i was also feeding my small reds ground shrimp and seafood mix when they were small then as they grew they started to eat tetras and larger shrimp then moved on to a gound fish/veg mixture that i make myself