You do realize that thereis a page with info on this ad idsoftware.com? No. Thought so. It is not that expensive, actually.
But then, why spend lotsa money on it after all (depending on the definition of "lotsa", of course)? There is the Torque engine, costs 100 bucks IIRC, and of course Quake and Quake 2 are GPL'ed - you can do whatever you want, you just have to release your modifications again. Check DarkPlaces, Tenebrae, Quake2Evolved, ...
The Serious Engine is quite cheap as well, and the one that powered Gore (forgot about the name). No need to spill a million bucks, if it does not have to be id or Epic, but needs to be closed.
Other GPL'ed engines include Crystal Space and Ogre. Use google.