4x4training.com also runs "basic" clinic, also at Hungry Valley, also for Jan 7th & 8th, and also by instructor for marines. Difference? This one will cost you $225 total (versus $375)..
Imho, not sure you need to pay for anything. Hummers are just about the most capable point-and-go as any 4x4 out there.
Join a dealer-sponsored Hummer Happening. You'll learn a lot. Better yet, go and play and experiment with fellow Hummer owners/enthusists. Yes, Hungry Valley is a great place to practice since you can pick and choose from many, many trails of varying difficulties. But the trick is practice, practice, practice.
My .02