There may be a small market for this, but there's a small market for business news and CNBC still makes money hand over fist (with paltry 0.1 ratings shares).
I don't think the size of the market is nearly as important as the SPENDING POWER of said market. Preowned Hummers likely appeal to mid-to-high end car shoppers, and that's a powerful demographic.
Regarding the domain, you may want to develop it. I think it would do very well with a car dealership that promotes it or by plugging it in (via affiliate links) to the used Hummer section of a car database.
Regardless, I think you'll get the most upside out of it by shopping it to car dealerships and/or developing it/promoting it on the net.