Dark meat chicken is usually cheaper than light meat and a good source of animal protein.
If you can tolerate carbs, dried beans, lentils, or split peas and brown rice are a good balanced source of vegetable protein and have lots of fiber. Carrots are generally a less expensive veggie and can be chopped up and cooked with the beans.
Healthy oils are very important -- canned tuna is a good source, but you don't want to it it too frequently (more than twice a week) bc of possible high levels of mercury. Peanut butter, in strict moderation (this is the important part!), is another source. I buy the natural kind but with your budget restrictions, you might have to buy based on price which is likely not natural. If you plan on eating salads, try to set aside enough to buy some extra virgin olive oil for them.
I don't know how often you will go shopping, but check the store specials and markdowns because those can be very good deals.
Good luck! It's hard enough to eat healthy without having to watch every penny. I hope you are successful!
Deborah: Hoping to earn the user name NoYoyoMa (maintenance start: 6/30/2014)