There is a lot more information about renting
ECVs in post #2 of the disABILITIES FAQs thread. You can find that thread near the top of this board or you can follow the link in my signature.
I know there are many companies in Orlando that do this. We may need 2. who has the best record out there.
There are a number of companies listed in the disABILITIES FAQs thread in post #2. They are listed there because DIS posters have reported generally good experiences with all of those companies over the years.
Some people prefer one company and others prefer another. The best advice is to contact some of the companies, check out their prices, their equipment and what your general feeling about that company is from your contact with them.
Not sure I want to deal with the buses, so what is the difference of renting at each park. If you hop, does that rental carry over to the next park.
1) You will save a bit of money by renting from one of the off-site companies compared with renting each day from the parks.
2) If you rent in one park, save your receipt and you will not have to pay again for rental in the second park
if they still have ECVs left when you arrive.
3) There are limited numbers of ECVs available for rental in the parks. They are first come, first serve with no ability to reserve one ahead of time. If you arrive right at opening, you should have no problem, but getting to a park later in the day may be a problem (whether you arrive late or park hop).
(If available) Is it cheaper to rent for length of stay from Disney? What is the discount for doing it that way. Thanks.
WDW does have length of stay for wheelchairs, but not for ECVs.
From what I had heard, they tried length of stay for a very short time, but were not able to guarantee that one would be available, so they discontinued the program.