My Surly Cross Check came with a 9-speed Tiagra rear derailleur, so it came in 9-speed a few years ago. It worked fine for a couple of years, and then I got a 105 derailleur for a good price.

I don't know enough about the road bike market to comment on what's decent for <$600, but another option would be to look for used bikes.

You might want to try to start another thread in the commuting forum. A few of us post here regularly, but more people would probably read a new thread.