If you are are recreational rider looking at used road bikes, you MIGHT be able to find something at that price with STI shifters (combo brakes/shifters). Or at the very least, what some people call Microshifters (push the brake lever to shift up, but push a small button with your thumb to shift down).
If you aren't set on drop bars, you'll find much more selection at that price point for a hybrid with trigger shifters.
If you are shifting a lot, you definitely DON'T want drop-bar or stem shifters...and you definitely don't want any kind of grip shifters that you have to twist.