How much are you willing to accept for them? That's the question you should be asking yourself.
Bingo. That is clearly one of the main criteria, however, you do have to anchor your expectations to current market prices somewhat, so subscribing to the Agon Bluebook service is certainly one way of doing that, although the caveat there is that the Bluebook data seems a little bit old and outdated, so that is not a great barometer of where more recent transactions have cleared. Triangulate between the minimum price you are willing to accept, bluebook data, and current Agon listings to see where you should settle out. Good luck.