[chumbucket]

Welcome to the site Jetstream. ;D
Sounds a bit high to me. You don't know how many hours are on that motor do you? A five year old motor and a three year old trailer (if in very good condition) might be worth as much as $6500.00. ??? ??? ??? (notice the questions!) That's allowing $5000 for the motor and $1500 for the trailer. What's a 1978 V20 hull go for? In very good shape, maybe as much as $2500.00. I don't know. Maybe I'm way off base, but I think it should be somewhere around $8000.00 - $8500.00. It would seem to me that for $10,000 you could find something newer??????
If you do decide to go for it and can come to an agreement, definately have everything checked out. And, if you're going to pay to do a comp. check on the motor, have them pressure test the gas tank too.
Good luck.