They come a lot cheaper than that. The biggest cost is the proprietary materials they use, I'm guessing it would easily add up to more than the cost of the printer over time. Servicing costs should also be pretty high.

I've compiled a list of most cheap printers (slightly out of date, I am going to add more soon): http://punkmanufacturing.com/wiki/

As far as usefulness, the open-source printers are not that different from the cheap commercial machines. A well-tuned RepRap should have comparable accuracy. The printing materials are a lot cheaper, as well as the parts (which you can print) and servicing costs. The commercial printers have better resolution, better materials and better software, at least at the moment, but I think that's going to change.