For a wheelchair, I rented a few times for my DD at WDW (she can't walk the distance that we do at Disney any longer due to Ehlers-Danlos Syndrome). Then, I found the exact same one we rented from an offsite agency (Apple Scooters) is on Amazon for like $150. I bought it and took it last trip with us, having to gate check it at the airport. I will save us in the long run!
For a wheelchair, you may want to look at Amazon. It may be easier to bring your own and cheaper in the long run (or at least you have a new one; the last time we rented the chair was in kind of bad shape).