Dylan,
With 7000 hours, it might be like buying a high mile BMW. Still life left with performance, but the cheapest operating time is long gone.
Is there a maintenance/ repair log?
IDK what kind of market value that chipper has, and its hard for anyone to guess, but I'd start offering a low dollar amount, relatively, if you like it. You can always go up. Consider what payments will be like for a new machine compared to an old one.