200 Town Hall
I’m thinking you’d have a hard time getting your hands on a town hall for less than $400, but I have not researched prices lately. Some of the other sets are still in production and not so valuable yet.
Anyway, those of you who are interested in making amusement park rides should take a lot at this eBay seller from France. He or she is selling both custom rides and the instructions for building them:
http://www.ebay.com/sch/johann.franckelemon/m.html?item=162206305194&rt=nc&_trksid=p2047675.l2562