I don't remember all the details so I could have missed or forgotten something but as I remember it you were a victim. A victim of at least a poor situation and bad luck or a bad dealer screwing over yet another customer. I think you got dealt a bad hand with Kashmir and can certainly understand it souring your taste on Hummer and the GM brand overall.
Parts for any vehicle these days are going to be expensive but yes, depending on what it is you can get raked over the coals for Hummer parts. The brand is dead but they have to supply parts for 10 years (if I recall correctly) after the end of production. That doesn't mean there are going to be a huge supply but what parts for the H3 are H3 specific that are going to be expensive? I ask because I am actually curious myself, not for you to make a list. Of those parts what are rebuildable? With H3s getting older there are going to be more an more used parts available through salvage yards. Maybe that is being optimistic but that's the way I see it. That's also coming from somebody that (keeping my fingers crossed) has yet to have any major issues with mine. I don't plan on ever getting rid of mine even with I get a new DD in the next year or so. Down the road I might find it very tough to find parts but it could also be like my Scout which is pushing 40 years old and I can find just about anything I need. Of course a LOT more Scouts were produced so I don't honestly expect it to be like that.
As far as what other Hummer to look at, depends on what you can do. If your budget allows try to find an '08 or newer but even an '07 gives you the benefit of not being the first model year. For being the first model year the '06 was remarkably reliable but with any first year vehicle there are going to be problems. That certainly doesn't mean that there can't or won't be with a later model but each year bugs get worked out. Of course with gas where it is you might be able to get a newer H3 for less that you could have 6 months or a year ago. Maybe it's time to move on to something else but you might also find love again in Kashmir II