Yep, mosey on over to ebay. I got a very nice 5-piece carbide burr set on there about 2 years ago for under $20, and I used them to port a head, exhaust manifold, and upper & lower intakes and they're still in good shape.
BTW- if you don't have it, in my opinion, the Standard Abrasives porting kit that Summit sells is invaluable when it comes to porting heads. It has everything you need. You can do intakes and other stuff with it too.