We have rented one numerous times for my father in law who is disabled. We have always been able to rent him one, no problem and he usually doesn't arrive to the park until later in the day and they have always had plenty. Maybe we have just been lucky. I think the cost is now up to around $34. You pay for the whole thing up front, plus a $20 deposit that is refunded at the end of the day when you turn it in. We have always been able to take it over to California Adventure as well. It can get tricky in the crowded walkways manuevering one around, but my fil has always managed fine. We were there over a very crowded weekend (Lincoln's birthday) in February and he still did fine. They have a little horn like thing in case you need to alert somebody they are about to run into you. The biggest problem is making sharp turns but he has gotten so used to it by now he is a pro! Some of the rides will have the scooter go in through the exit, some rides they can go through much or all of the que. Having a scooter can make things more challenging but can be a real lifesaver for the elderly in particular! I would arrive early to be safe so that you know you can get one for sure. But as I said, we have never had a problem, they usually seem to have plenty to spare. And yes, they are rented just as you enter the turnstiles by the stroller rental. They also have wheelchairs there as well.