The first thing a dermatologist would have you do is a food elimination trial to see if there is a food allergy or if it is some other kind of allergy. To do this trial, you need a food with very simple ingredients, preferably with an unusual protein source. Since Natural Balance has been a part of the recall, I'd suggest one of the Wellness Simple Solutions foods. I know they have dog varieties, but you'll have to check on what they have for cat varieties. Pick an unusual meat (something you cat hasn't had) and go with the formula with the strangest grain, if possible. Feed it for 6-8 weeks exclusively with NO other treats or anything with a flavor in it. Also give only distilled water. If you see improvement, you know you have a food allergy. If you don't see improvement, odds are it is not a food allergy and you will probably need to do testing. Steroid shots are not a long term solution, and they will cause more damage in the long run (in addition to becoming less effective).
If you do so improvement with the food switch, gradually start bringing other whole foods into the diet -- a little chicken breast for a week, and if that works out okay, maybe try some beef for a week. Keep adding things in until you find something that doesn't work for your cat.
I have only done this with dogs. I have one who is an allergic mess. She did not have a food allergy, which we determined from the food trial, but we had the dermatologist do a skin test (and it wasn't $500-$800 for the test -- but with the serum added in, too, it was closer to $500), and she was allergic to a lot of pollens. We give her immunotherapy injections every 10 days. It has improved her quality of life be leaps and bounds, and I would recommend it highly if the food trial yields no results.
Also think about what has changed in your household -- new cleaners, detergents, pest control treatments, etc. They can be sensitive to these things. They can also have allergies to fleas or dust & dust mites. My dog is allergic to all 3 of the those! Flea allergies simply require application of Frontline every 3 weeks instead of every month. Frontline goes down to 75% effectiveness after the third week, which is plenty for most animals, but not enough for a flea allergic one.