Looks like a cool ride. You should have some wiggle room there with the price I am betting.(depends on how much $$$ the dealer is into the truck) Figure a couple $K for extending the warranty(if you plan on it, but it makes a good negotiating tool being that it's soooo close to the 50K mile mark!), maybe 1.5K or so for TT&L. I would suggest to toss out the interior/exterior/underbody protections they will no doubt offer. From the pics, it looks like a 2007.5. I *think* that's when Hummer starting putting the window/lock controls up farther at an angle on the driver side arm rest. There should also be more clearance for the seat controls. If the dealership is worth their salt, they are going to push an extended warranty on you like CRAZY. They will of course make it sound like it's gods gift to warranties, and you would be the dumbest person in the world if you didn't take it. If you have the funds, it's better financially to pay the warranty outright, rather than financing it in. $8 difference a month sounds good, but paying $1500 cash rather than $2K financed sounds better to me!
Check to make sure the battery and fuse box are in plastic, pseudo sealed containers. Check the hood luever(sp?) for a tight, snug fit, as well as the sun roof air deflector. If possible, see if you can take it through a car wash to check for leaks.

All I could think of during my lunch break. Good luck on the H3! They are sweet rides!

Bryan B.