I lived in Durham, NC for 7 years, and found RDU parking to be cheap in the remote lots, although inconvenient. The only possible alternative I can think of that is both inexpensive and close is the National Guard Aviation Facility. If you are a member of the armed forces, there is a slight chance you could schmooze the guards there to let you park. Of course, you would still need to get someone to drive you from their parking lot to the terminal.

I know of no airport that has any close parking other than at their official lots.