Pcnation has a Tyan model s3970G2N-U-RS server board for $242 that has 2 sockets and 8 ddr2 slots that should work fine. You have to use bios version 2.02. Don't know if the board will post using barcelona without a bios update first. Registered ddr2 memory is required. Crucial carries a 2 gig kit of registered ddr2 pc4200 for $140. This board isn't designed for overclocking. If you want to overclock, wait for phenom. Server boards in general are designed for stability, not performance.
Newegg has the 1.7 ghtz barcelona for $239. It runs at 55w, which is about half of a b3 stepping q6600. But I haven't compared benchmarks. Hopefully, phenom will be out in early 08. The tyan board I quoted was one of the cheapest available. So you're looking at about $620 mimimum for the cpu, board, and 2 gigs of memory. Heatsink is extra. Msi has a single socket barcelona board due out soon, but I doubt if it's cheaper than the tyan.