As you are likely already aware, your darkroom space will dictate some of the terms for a "new" enlarger. How much height do you have to work with, does it need to be moved, bench space, etcetera. As others here have noted, lots of things are available in local deals, as well as fleabay. One source might be your school system or closest college. Many things are surplused out and sold to the public.
Think expandability as well for the future. As an example, the B22 is a great enlarger, but find a dichro head for it when you want to move beyond gel filters or into color. I will admit that I am biased; my standardization has been Beseler and the 45M series. If you do not plan to move into 4x5 in the forseeable future (or ever) the 23's are a great deal. A quick check on fleabay will show you that every conceivable carrier, head, and accessory is available in plenty and for great price if you are willing to bear out a few different auctions on similar items. In the same vein as the 45M, are Omega enlargers, and as others have pointed out, Leica, Durst, etcetera. Some of these can get expensive in terms of accessories. I dumped a Laborator 1200 because of that... Also, beware great deals on older enlargers such as Federal, Elwood, etcetera unless they are selling the carriers and other things along with them. It's getting harder to find parts and accessories for something that has been out of production for 50 years...
