Yep. It's pretty crazy: part prices are actually almost tracking Moore's Law.
There are also newer processes that are much more expensive. If you're checking out something like an Objet machine, or something like EBM, you're still going to be looking at an upper 5 figures to a mid 6.
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.
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.
Most of those materials are reverse engineer-able, though. This has a significant impact on the big manufacturer's bottom lines... they derive most of their profit from materials, just like regular printers.
You can probably get a spec-sheet for their proprietary materials if you ask. You might have to reverse-engineer cartridges with security features though.
The Fab@Home guys are trying out various different materials, since their syringe-based extruder allows more flexibility than the RepRap.
The biggest cost is probably the manual labor that goes into finishing a part. 3D printers are hardly analogous to the current state of paper printers: all of the technologies require some form of post processing (cutting away supports, curing materials, sanding, etc.).
Most of the discussion I see about 3D printers ignores the significant amount of physical effort you have to put into a part if it will be used for anything (and depending on the method, just to see the part).
Generally, those from the engineering community sneer at the MakerBot and the RepRap. Just listen for the word "tolerances."
Now, they're totally right: the home printers have a significantly lower resolution than the professional ones. But unless you're making professional grade parts, you probably don't care, and they use the same materials. (I'm assuming you're making the comparison to other FDM machines.)
Assuming the tolerances for the cheap 3D printers will improve, isn't this a classic case of disruption we are seeing here?
Sure they aren't great enough for everything yet, but there has to be things you can create even with the cheap bots that are good enough to be useful.
I expect it to be similar to what happened with the printing press and computers in that you'll be able to download (/pirate) actual objects. The revolution will be huge.
The best machine gun in Mass Effect 2 has "Fabrication Rights Management" technology which prevents you from printing one for each member of your team. I doubt real-world engineers for companies whose products would be most affected by downloadability are too far behind.
I'm also assuming that you're talking about FDM, like the MakerBot/RepRap. If you're talking about a different process, well, then it's different.