Are the other, cheaper master cylinders new or remanufactured? Bear in mind that some remans are basically junkyard pulls that are cleaned up and with some known-issue components replaced. They're not necessarirly tested or thoroughly examined either, and the price one pays at the parts counter often reflects the level of work done on the part.
It's possible that he's been burned on labor for warranty-replacing too many not-OEM parts, and for the cost difference it's not worthwhile to him.
It's possible that he's been burned on labor for warranty-replacing too many not-OEM parts, and for the cost difference it's not worthwhile to him.