Mr. Bill, just doing a quick search of a used vehicle similar to yours (since I really don't know all of your options)... the prices 'retail' from from $34,900-$37,995 (I found 4 units).
The new 'used' coach that you found, I found a new '15 for an advertised price of $119,900 (again, not knowing the options....so it could be apples and oranges). Those seem to MSRP up to $176,000.
I bet they will offer you around $22,000 for yours and their price will probably stay firm at $99,000 which doesn't seem too bad with a quick look on the internet.
Let us know what happens.
Good luck,
MM.