We have a German Shepherd with a very sensitive stomach - we have fed Taste of the Wild salmon formula, EVO poultry, beef, and fish formulas, Wellness Core poultry, and Orijen poultry and fish. They are all fantastic grain-free foods with human-grade ingredients. Orijen is our favorite, but we feed EVO most often because it's the easiesr to find. EVO, Orijen, and Wellness Core all run about $55-60 a bag for a 30lb bag, at the stores we shop at. Taste of the Wild is a bit cheaper because it's lower protein.
Good luck finding a great food that works for your dog!