Ahh, here's the schedule with costs.
http://www.resortseastchicago.com/transportation.shtml
It says that you need a valid "R card" and ID to get the bonus dollars back when you arrive at the casino, but it's been my experience (back when it was Harrah's) that you could get on the bus with your ID and get a membership card when you got there to get your bonus money back.