Translation: Your dog is super prone to allergies.

A daily antihistamine such as Benedryl will help... after you get things under control. The skin by now probably has an infection which will only cause the itching and allergic reaction to increase. You will need to treat the infection internally as well as externally, or with antibiotics. Also short term Prednisone therapy 1-2 weeks will reduce the inflamation. Remember to taper off when on Prednisone. Cost wise the Prednisone isn't much. Also an antibiotic such as Cephalexin is relatively cheap.

You might want to stop by the Vet's office without the dogs. Ask to speak with the Vet and inquire about Prednisone and antibiotic treatment. Since you were just there, they can't hit on you for a visit, which should save some money. If they refuse then find another Vet, and tell them you want to help your dog, but can't afford hefty diagnostics etc. The goal again is to get the Prednisone and antibiotics. After which Benedryl to control the allergic reactions.

All of this assumes your dog isn't suffering from hypo-thyroidism or some other skin condition.