I think your price is about right (but I'm a little biased, owning a Tristar myself) but you will need to be patient to get it. I don't think I would limit my time frame to the end of June. Keep a for-sale sign on it through the season. Maybe someone at the lake will see it and want it. As far as newer Mastercrafts, you have to go all the way to 1993 to get fuel injected motor and those generally sell for $10k or more in condition similar to your boat. The $6k range Mastercraft is typically going to be a Prostar in less than average condition or a 1980's model Stars and Stripes.
Try to pick up a used pylon extension. It will add interest from novice wakeboarders.