What dog food can I give my Cockapoo who suffers from food allergies?

The vet believes my dog may be allergic to the typical meats in dog foods: chicken, beef etc.She suggested that I find a dog food with more unusual meats that my dog would be less likely to be allergic to. Is it true that most dogs with allergies are actually allergic to the meat instead of the added stuff? Have you ever had a dog with skin allergies, frequent ear infections or frequent infections in general? What dog food worked for you? Do you know of any dog foods with unusual meets such as kangaroo that have worked well for you? Also, as I am currently searching for a job I really can not afford to spend 40+ dollars on dog food every week. I love her dearly but, I just can not do that at this time. Does anyone have any ideas as to what I can do to help her stop itching and getting on a diet more suited to her needs? Her problems include itching,many ear infections and infections under her tail. The vet told me that " food allergies often show problems from the ear to the rear." She was right in this case! Also, is feeding her items at home okay until I get her a better diet? Lately I have been trying to feed her things like tuna with rice, green-beans and apples. Any help would make me smile and make my dog's tail wag! = ) She is a great dog and I hate to see her suffer.