First try readjusting the parking brake. If that does not work, the parking brake shoes have completely worn down and they will need to be replaced, I believe fastlane should have the parts for around $30 or so if you do it yourself.
Not sure what a mechanic would charge.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record