I would start calling your local print shops... I found a very nice tabletop mercury unit in my area for $300. Some shops are willing to "give" this equipment away because they don't use them.

You can also try these sites for used pre-press equip:
http://www.printrade.com/classified/cats/3500.html
http://www.print-world.com/classifie...p?categoryID=5
http://www.prepressforums.com/forum/items-sale/

I am very pleased with my mercury bulb unit, especially since the replacement bulb was $35!

John "Alpha Flying Monkey" Moore