The prices are pretty much always going to be less expensive per day renting from one of the off-site places than renting per day from the parks.
Of the off site places, Randy's is normally one of the least expensive. A big part of his reason for being less expensive is that you must be there for delivery and pick up. There is less chance for damage doing it that way and you can get instruction on how to operate and care for it.
The parks can't prevent anyone from bringing in an
ecv from outside. If you need equipment like that, they can't say that you need to use theirs. That would not be allowed under the ADA (Americans with Disabilities Act).