Both Ebay and Amazon are selling Marin bikes right now for pretty decent prices. They are all coming from a company called Crosslake Sales. Though they are all Marins, there is a pretty large selection. I just picked up a Rock Spring Comp for about 1/2 retail price.
Here are a couple of examples in you price range:
http://www.ebay.com/itm/2013-Marin-B...item4d16814cf5
http://www.ebay.com/itm/2013-Marin-B...item4d163e0202