Where are you from? Cheap is a relative term.
Roo is cheap, high in iron, protein and low in fat. The mince is easy to cook, the steaks are a bitch.
Chicken breast is about $15 a kilo, can find it cheaper in bulk or on sale.
Rump steak anywhere from 12 - $20 a kilo. (a kilo is 2.2pounds)
Beef mince $10/kg.
Free range eggs $5 a doz.
We eat a lot of lamb - anywhere from $10 - $25/kg depending on the cut.
Lots of fish around, Salmon is $20-ish a kilo, cheap white fish $15 a kilo.
You can buy mass gainer proteins for $100 for 3kg in a shop, cheaper online.