Actor/Politician Arnold Schwarzenegger is partly responsible for the Hummer being sold to civilians. He drove a military version during the filming of Kindergarten Cop and was so impressed he urged the company to sell them to the public. The civilian version is similar mechanically to the military version, but without the armored protection on all sides (including the undercarriage).
Engines on the H1 ranged from a 5.7L Vortec V8 to a 6.6L turbo DMAX Diesel V8. Emissions standards that took effect in 2007 caused production to cease on this vehicle, the largest one produced by Hummer, which is currently a division of General Motors.
The H1 can still be purchased through fleet sales, which circumvents the emissions standards. In fact, purchases of H1 and even H2 vehicles can sometimes be tax deductible thanks to our rather screwy tax system.
With a retail price of around $80,000 for the open top and $90,000 for the closed wagon, the Hummer H1 is not cheap. You can find them used for a fraction of that price, but be prepared to drain your credit card when you go the gas pump. At current gas prices, a fill up could cost $100 or more, depending on location. My advice is to save as much money on the original purchase by buying used. There are plenty of listings on eBay, take advantage of them.