Ebay and autotrader are the prefect places to watch the prices.
I would recommend getting a login for
http://www.hummernetworkforums.com/ and check out the H1 forum. There is also a knowledgebase where you can look up additional information about buying an H1 and what to look for.
Members will post H1's for sale as they some across them and will give you feedback on H1's people are looking at. Post this same info there and you will get more feedback.