See the below site for how to convert server power supplies for RC use. You can use one for 12v output or two for 24v output. The same two PS setup can supply both 12v and 24v. These are the exact same PS units that MaxAmps is selling. If you do it yourself you can pick up two of the PS for $30 - $40 on ebay.

http://sites.google.com/site/tjinguytech/my-projects

Also, checkout the battery forum at rcgroups.com. There are a couple huge threads on converting server power supplies.