Here in the Seattle area, I've contacted quite a few shops (dealers, speed shops, differential shops, etc.) and the average around here is about $500 to $1,000 for parts, labor, tax, etc. I had a well-known speed shop in the area quote me $1,200!!! I ended up paying a grand total of $480 for parts, labor, tax, etc. at the Ford dealership I work at (but that was at employee rates).
Most I've ever paid to do a gear swap is about $850, but that one also included correcting the speedometer by buying/installing a Dallas Mustang Speed Calibrator as I didn't have a handheld tuner for that particular car.