Proteins are made up of amino acids; a "complete" protein is one which contains all the amino acids needed by the human body. Meats and fish are complete proteins, but they can be expensive unless you are able to grow or harvest them yourself. Freeze-dried meats, as you mentioned, are particularly pricey.
It's probably too late in the season for this, but if you have freezer space you could try putting up a notice at your local custom butcher shop that you would like to buy "freezer cleanout" from someone who needs to empty their freezer of last year's deer meat to make room for this year's deer. We made it through two particularly difficult winters that way - one person even gave us all his old deer meat for free. It had been well-wrapped and deep-frozen and was some of the best deer meat we ever tasted. If you find an inexpensive source of meat and don't have a freezer, you might consider canning it or making homemade jerky.
Fortunately, meat isn't the only way to get complete protein in your diet.
Read up on complimentary proteins ( two or more incomplete proteins which, when consumed within several hours of each other, will undergo recombination of their respective amino acids to provide the body with the equivalent of a complete protein).
To get this complete protein equivalent, just combine certain plant foods as follows -
Select a food from the "Bread, Cereals and Grains" Group below and combine it with a food from the "Legumes" Group or the "Nuts & Seeds" Group :
Breads, Cereals, Grains Group
Includes breads, crackers, pasta, flour, rice, oats, wheat, corn, barley, other whole grains, etc.
Legumes Group
Includes all beans, bean sprouts, peas, lentils (stay away from a soybean-based diet, however, as there is evidence that hormonal imbalances and other health problems may result).
Nuts & Seeds Group
Peanuts, cashews, walnuts, pecans, hickory nuts, etc., sunflower seeds, pumpkin seeds, sesame seeds, etc. (#10 cans of peanuts are about $6 at places like Sam's).
One example of a complementary protein meal that most kids like is your classic peanut butter sandwich, or peanut butter on crackers. (A breakfast favorite at our house is peanut butter on buttered whole wheat toast).
Other common examples:
Beans & cornbread (or biscuits, frybread, etc)
Beans & Rice
Bean Soup or Split Pea Soup & Crackers
Bean sandwiches (as described by FollowTruth, or just spread canned, condensed "bean with bacon" soup on some bread)
Macaroni & Cheese, Cheese Lasagna, Chili Mac
Hoppin' John (Blackeyed peas and Rice)
Tortillas w/refried beans (top with cheese)
Granola with yogurt or milk
Rice Pudding
Some Trail Mixes
Don't forget to stock up on seasoning for your bean dishes. For a low-cost bean seasoning, try purchasing cheap "bacon ends" at your grocery store or butcher shop. Freeze the bacon in small meal-sized batches - allow approximately a quarter pound of bacon per Lb of dry beans. Ham hocks are even better, of course, but since they contain more meat they're more pricey.
For a cheap complementary protein/energy snack, let the kids mix up a batch of "Power Balls" The ingredients are fairly inexpensive and easily stored.
Blend the following ingredients and shape into balls slightly smaller than a golf ball:
1/2 c honey or molasses
1/2 c peanut butter
1 c dry milk, non-instant preferred
1/2 to 1 cup raisins
Roll the balls in powdered sugar or hulled sesame seeds to keep them from sticking together. Store in refrigerator.
