500 $ ...
Yamaha P80 were/are pro stage pianos and came in pretty good shape with weighted hammers and good piano sounds and stuff. You'll find them easily e.g. ->
here .
Edit: Oops, just saw you've already made up your mind. And, indeed, a new
Yamaha P95B likely is a way better decision than a used P80. I am quite confident it's a very good choice. Best wishes for your son.