What little of it the guy shows looks pretty nice.
Seems odd that it would need the left rear floor replaced, as the rest doesn't appear rusty; I'd expect the lower rear quarters or spare tire well to go first.
I don't know if KY cars get rusty, but maybe the car came from somewhere else ?
Without more info & photos, he may not be too far off in price, if you're OK with the Slant 6 or have another drivetrain to swap in.
You can always offer $7500 - $8500 depending, and haggle away.

The little house on stilts in the background is amusing !