51 cm Road Bike

Hi Everyone,

I'm a runner and I'm looking expand and get into some duathlons and maybe some triathlons.  Anyone selling a 51cm road bike?  I'm not looking to spend too much since I'm just a beginner.  My budget is around $600 for a good lightly used road bike.  I anxious to get my training started for the spring!

Thanks!
Tina