Cheapest place? Probably an on-line auction like eBay! Another option is your local proshop. Put your name in for a good used bow. There are guys always upgrading to the newest thing and you can sometimes pick up a year old bow for hundreds less.

A word of caution with on-line auctions...you better know your proper draw length, check the sellers feedback, and ask very specific questions about the bow your looking at before bidding.