While we were up in Seattle last week, Pete and I found rubber base molds made by a local company. The concept is that you take a normal plastic base and spread a layer of modeling epoxy (green stuff or similar) Then press the mold onto the base. Each mold is $5. Takes a little practice to get the mold to set just right (make sure to watch the instruction video), but it is a cheep alternative to resin bases.
Check out the molds and the instructions at the company's website: http://happyseppuku.com/
Picture is of our first few attempts.