What is your budget? Used is going to be your best bet. 105 if you can find it, 105 rear/tiagra front will probably be OK. If your budget allows, you could go for a bikesdirect bike: brand name components (mechanical parts are the most important) on run of the mill, no name frame and bits. Those don't matter if you are training. Incremental changes in your riding performance is what matters unless you are actually racing.