Best dog food for chihuahua that's had stomach surgery?

Older dog chihuahua, Prissy about 10 yrs old, 10lbs, had stomach surgery several years ago (she was chewing on everything and swallowed some household items--that's all OK now) Vet recommended she eat food only from his place. Was on Prescription Diet IE, she's on Purina EN now. She & other dog, Lucy (6 yrs old 4lb) like it OK, but it's main ingredient is corn and it's awfully expensive. Prissy is extrememly picky, Lucy will eat anything. I need a dry dog food that is formulated for stomachs and perhaps a bit cheaper. Something with small pieces for small dogs. Any suggestions? We have a Petco & PetSmart here, as well as Wal-Mart & Target. I'm tired of shelling out big bucks to vet for corn dog food.