Omega B22, or better yet, B22 XL: common (perhaps the most common enlarger ever), cheap (if not free), and good enough.
This being said, a brand new (imagine that!) Omega C-700 is not a bad deal at all at under $400 from Freestyle with a lens (Arista 50mm f/3.5). You'd need to get a neg carrier and a lens for medium format, however, and they are $70 for the carrier and $60 for the lens (again, Arista brand).
A timer would also be nice, but a Gra-Lab processing timer (dirt cheap if not free), while a bit annoying to use, will do the trick at first.