what's a (dog) mom to do

Over the last few weeks we have been back and forth to the vet with Magoo. Because he lays awake itching and scratching all night long. And we figured it was long overdue when we noticed one day that he had chewed all the hair off his tail and was starting to chew on the skin on his belly. Poor little guy. The first appointment they gave him a few shots, next time they ruled a few things out and gave him some more shots and then last weekend the vet decided it is definitely a food allergy. So now he has to eat prescription food and he cannot eat anything else. Not only is he banned from eating all people food, but on top of it we are rationing the prescription food because it costs $60 a bag.