The cost between a low-temp and high-temp dish machine is pretty tit for tat. Hot water can cost you, yes, but in many cases the chemicals for a low-temp can be just as expensive.
If you purchase a high-temp dishwasher you may need to purchase a booster heater as well if there isn't one already built in to the machine, which can defanitely get expensive. On the other hand, the harsh chemicals used in a low-temp machine can damage frail dishes like flatware if they are not balanced properly.
Do some research and don't rush into a purchase. I agre with GBJordan that renting may be the way to go.
We sell Jet Tech, Moyer Diebel and Meiko. From what I can tell our customers really like the Moyer Diebels. No experience with Hobart dishwashers but I've always heard good things about the Hobart brand in general.
Here's a blog that I recently had to write for my company. I had to research all the different kinds of dishwashers and how they work. It may help you determine what kind you need.