Thanks all for the responses.

I decided against buying used since I had no idea what I was looking for in terms of frame size etc.

In the end, I bought the K2, which was on sale at $500 (LLBean has the same model on their site for $649, so I knew it wasn't a "fake" sale). It felt great, but then as a complete newbie, I don't really have any idea. All the other road bikes they had in stock were pretty much all over my price limit, so I took risk.

HipGnosis6 - I hope your concerns about the K2 brand will not come back to haunt me!