Hi -
As far as I know, there is no pass you can buy to park at WDW, but:
1. You only have to pay for parking at the first park you enter each day. ($7 as far as I know). Re-entry, or moving to another park will be free PROVIDING you ask the attendant when you enter the first park for a pass to put on your windshield. (I think that's how it works - I've never had to do it, but you won't encounter an attendant on your way out, so I can't imagine where you would get the pass, except on your way in.)
2. You are entitled to free parking at any of the parks if you are a Disney resort guest, or if you have an annual pass. We have annual passes, and routinely drive to many of the parks instead of taking the Disney buses, just because we prefer the convenience of having our own car, and not having to wait for a bus. If we can take a boat or monorail, we will. If we must take a bus, we drive. Not everyone's strategy, I know, but we've been happy with it. Hope this helps.