Unfortunately the subject is a little misleading, because of how hard it is to get the particular keyboard I'm talking about. I'm lucky enough to have family and friends in Korea, and there was a company (which looks like it went out of business) called ARON Tech or ARON Digital that made mechanical keyboards. One of their models was an ergonomic (split middle) one, which I managed to snag. I love it. When I purchased mine, it ran for about $60 after the exchange rate. The USB version (which is what I should have gotten) ran for about $80, IIRC. Unfortunately it is supposedly tough to find these keyboards in Korea now.
You can see a photo of the keyboard here: http://fv521.egloos.com/2791639
Web archive also has a good set: http://web.archive.org/web/20030202083656/http://arontech.com/
The reason I mention this is because it looks like ARON just farmed out their manufacturing to a Chinese firm, and it appears that you can still get these keyboards:
I'm also interested in a mechanical ergonomic, specifically for the USB interface. My current mechanical ergo is PS/2, and while it works great, and will for the foreseeable future, I'd also like to have a USB one.