$500 for a refret seems a bit steep to me, especially for a guitar without binding. The fact that it's a vintage piece shouldn't make the job any harder or more expensive, but you do want a very experienced luthier to do the job. There is always a premium for a skilled technician that's in demand.
500$ for a refret does sound like a rip-off to me. I'm on another continent all together, so the prices may be lower down there, but even 200 quids for a refret by a reputable luthier would be considered expensive.