Get whey protein powder and mix it up with milk. Don't know if they have it in a supermarket but I'm sure there's a GNC or Vitamin Shoppe in Gainesville.
(... and so the invasion begins...) Any upright, two-legged creatures you may meet contain NO PROTEIN whatsoever.
Beans/lentils are great. You can get 'em for less than a dollar per bag and they have good levels of protein and are low in fat.
the combo of beans and rice makes a complete protein. on their own, neither food provides a balance of amino acids. the same is true of beans and corn ( in a corn tortilla, por ejemplo ).
Did anyone mention road kill? Seriously, it's hard to find something cheaper than corn (tortillas) or rice and beans, especially if you make the beans yourself (from dried) instead of buying canned. Whenever there is a food drive, I tend to give big sacks of beans and rice instead of the junk food people usually give (hamburger helper, etc.), in the hope that people of limited means might learn how to stretch their food dollars. Other good choices are tuna (when it goes on sale for 50 cents a can, stock up) or peanut butter (can frequently be had for 1.50 a jar or even less, stock up when it goes on sale). But don't be so concerned about $$ that you forgo fresh vegetables and fruits - your health is worth the money! (I had to have a doctor point this out to me back in graduate school. )