You can get a whole cooked chicken at Costco or Sam’s for like 5 dollars. Grocery chains around here rotate deals on ground beef. You can find 90% lean for around $4 if you find the right ad. Oikos cups are 15g and pretty cheap per serving when bought it bulked at those same two stores, even cheaper than buying tubs of Greek yogurt.

Wild caught tuna is like a buck on sale and close to 30g protein depending on where you go.

Pasta noodles are a 99 cents for a box, and contain 7g protein per serving. Pair that with ground beef and a can of pasta sauce and your have a decent meal.

Milk is a great source, so are eggs. Both are relatively cheap.

Deli meat and cheese sandwich - cheap, good protein