Well said Larry! you must be a fellow Engineer. Mikeyr I wold suggest doing what Larry said as this is your most cost effective solution to your problem. Just make sure you make your piers the correct size according to a soils report!
Most of the Driveways that I've done had a 4"-6" concrete slab underneath it and we would level it with sand. If not then we would have to have 8"-10" clean gravel fill and then 1"-2" sand. A sloped drive shouldn't really be a problem unless its a crazy slope. But make sure you glue the edge...