A great place to look is your local craigslist site. What I would suggest is to set up your budget before you start looking. People will try to sell a GCII in horrid condition for $1500 when it's really worth at most $500, but you will also find people selling a GCII in great condition for $900. A good option would be to start looking around for a qualified table mechanic who you are going to pick to move/setup your table. When you find something you think you might like, have them go with you to inspect it. You can ask around in the Mechanics section of AZB or look at the sticky thread in that forum for mechanics that might be close to your area.
The hard part with used tables is there are so many different variables to take into account to find out if it's a good price, such as:
* Are the rails (rubber) in good condition?
* How is the cloth condition?
* Are there any chips in the slate?
* Are all the parts there?
* Is the slate warped?
* With the older Brunswick's you also have the question of "is it slate or brunstone (brunswick's attempt at a slate alternative, hint, it's reddish colored)
* If it has a ball return, does it actually work?
And there is of course the simple cosmetic variables.
In addition you might decide that you want new cloth and new rails put on no matter what the condition is, in which case you can ignore those parts, but assume about $500 to have that done.
Brian