$350 is probably right in the ball park...you could offer $300 and see how it goes, if it is not in excellent shape i would probably pass. It is not the arcade quality but it is very good and far and away better than anything you would get at a dept store for twice that. I owned one and it played well, i did eventually upgrade to the "coin-op" when one showed up on craigslist but then sold the storm II for $350 and do not regret starting with that.
When you do pick up a table make sure to get the "foos lube" as it is a common mistake people make to try other lubricants that have a negative affect on table performance.