Hey guys, I've been buying and selling on Ebay since 1998 and since day one I've been keeping and constantly updating a database of all model prices. I can tell you a good asking price for pretty much any synth that isn't super-rare.
I track averages, means, medians as well as upward and downward trends.
Why do I do this? Because I buy low and sell high after fixing up or reconitioning if needed, providing manuals and other materials that weren't included, etc.
So just ask me if you need to know a good price on your gear or are looking to buy firstname.lastname@example.org