Mark,
Have you tried running a Vref valuation? The price might not be exact, but it will give you an idea of the ballpark. Many people will run a Vref on a plane to come up with an offer. Your plane might be much better than average and you can explain that when discussing the price.
You need an AOPA membership. You can then go to
https://m.aopa.org/members/vref/default.cfm
