There's lots of privately owned parking out there, even around airports, but nor market for it. What about a web market?
Imagine, if you owned a parking space, you could file it in a database. People going somewhere hard or expensive to park would go to the web before the trip, enter the address, and get offered a spot near their target with a rate. This could also include commercial lots with spare space. If not at the web, you could call from your registered cell phone for a small extra fee while driving to your destination.
I see this particularly useful near the airport. You would be given a private spot a short cab ride from the airport. On the web, you would get printed directions to the spot from you and from the airport, and you would get a list of cab companies with pre-negotiated rates. You would phone one on your cell phone, or in a fancier system, the network would arrange it for you. Coming back you would just find any available cab -- faster and more direct than the off-airport parking lot shuttles.
When you got to your car you would call a number from your registered cell phone, and it would see the caller-ID and check you out of the spot, freeing it for somebody else and billing you.
The rate you pay the private lot owner might be lower the higher the cab fare is to keep the cost roughly flat. For many lot owners near airports (businesses, hotels) it's found money. They would get web access to the licence plates of the cars that should be in the spots, and could spot check to assure compliance.
Yes, it takes time to go to a web site before you leave your house, but you waste much more time hunting for parking in the tough areas.