The Unreal Development Kit has been released for FREE for all non-commercial purposes!!
http://www.udk.com/
Now I'm not suggesting a move to the UDK. Mainly because it's based off of the UT3 engine which would probably require a complete rewrite of the entire game and require a fairly decent computer to even play it.... But is still cool none-the-less...
Too bad they didn't release the Unreal 1 or 2 engine also....