Driving on the other side is really not much of a problem--you won't even notice it after about 2 minutes. I travel back and forth monthly and it is a fairly easy adjustment.
Turning is the only thing you need to look out for. You're used to looking one way for traffic but it is coming from the other direction, so you have to make a mental note whenever you turn to look both ways a couple of times, just to be sure.
Orbitz.com has some pretty good comparisons of all the different rental rates for cars.