I went through this last year. Do NOT buy via eBay unless you are certain the vendor is reputable. Do NOT pay the dealer -- the alternator you will get at that price isn't even new, it is rebuilt.

Go to your friendly local alternator rebuilder and pay him $200 or so. Then install yourself. One thing to be aware of -- the "picture book" reference some of the rebuilders use to determine clocking may be wrong. Make sure he marks the top and bottom portions before disassembly and puts them back together the same way, otherwise you wont' be able to reinstall.

Happy motoring.