Absolute beginner, what's the best road bike I can buy in the $400-600 range?

Hey all, wanting to give road biking a try as I'll be in a nice area this summer (Chicago) without much to do. I'd really like to spend around $400-500, but I'm willing to go up to $600 as an absolute maximum (broke-ish college student). I've been reading as much as I can, but to be perfectly honest a lot of it is very overwhelming.

Considering I do not care about brand at all and just want a decent bike, I was looking at bikes direct but since I don't really know the components I couldn't really tell what was a good vs. bad bike there. Any suggestions at all would be really helpful. I know that used will probably be recommended, but I'm not certain I could distinguish between a well and poorly maintained bike if I were buying used. Thanks in advance!