We bought the NordicTrack Commercial treadmill from Costco - it was about $850. They don't have it online, but it's still in the stores here in CO. I think it is a great deal. It's a lot better quality than the cheaper new ones you'll find, and probably just as good as the $1,000+ machines. In my research, I found that the higher priced ones usually just had more programs. If you find one with a 3.0HP motor, it's probably pretty good.
Definitely keep looking on Craigslist - you might find a great deal. Just research the machine before you go see it and then be sure to try running on it before you buy it. www.treadmilldoctor.com is a good website for reviews.