Buy the bike, put everything you don't want on CL/eBay. When I went looking, there were framesets going used for $600-800, but I got a new complete 105 for $1100.

The trap you can fall into here is that instead of taking the time to upgrade the bike to the parts I wanted, I just started riding it so I now have a 105 group with 2000 miles on it, and a wife who won't let me spend the money on a Campy group.