Fox & Obel is set to open in the loop some time soon, but I don't think their prices can be considered "good." I've only been to
Green Grocer once, but they may be closer to what you're looking for. Also, there are two great Farmer's Market in the loop: Federal Plaza on Tuesdays and Daley Plaza on Thursdays.
Maybe someone with experience shopping at some of the restaurant supply places in the West Loop can offer suggestions.