What is an affordable frame primarily for racing? Aluminum or CF?
What type of racing are you talking about? Time trials, road or criterium?
If you want cheap, Cannondale Caad5s are great criterium bikes. they have fairly steep geometry and high bottom brackets which lend themselves nicely to races with lots of corners. Aluminum Giants are pretty decent also without costing you a fortune.
Orbea Enol roadie, Fly Micromachine BMX, Fort Track fixed
I'm no expert, but the Guess RB1 is pretty cheap and great looking too. Cycling Plus (top UK mag) awarded it a Bronze in their 2003 Best Race Bike catagory and Gold in Best Budget Racer. I think it's about £500 frame and fork, which is around $1200 US.