Getting a road bike

I've been looking for a road bike this summer, and was thinking used and watching craigslist and local bike shops. It's hard to find used at any of the bikes shops within 20 miles of here, though. And I've been warned off buying used not from a bike shop unless I really know the minutiae of bicycle engineering, otherwise I might add another $300 onto a $125 'steal.'

So I started looking new as well. Turns out drop-bar road bikes like I like are entry-level at about $500-$600 for Trek, Raleigh, etc. Or about $200 for non-branded Schwinns and the like that get sold through Amazon, Target and Walmart.

So the question became: Buy the cheaper bike, use it to train for this first triathlon and consider an upgrade as a reward for finishing next year, or put more money in now on the nicer entry-level bike and count on it being better for training and keeping me motivated?

Still torn, have advice from both sides and want to be riding now. I'm going to Milwaukee on Saturday, and hope to check out just a few more bike shops, and maybe find a used or closeout deal. I would love to be formally bike training by Monday.