I expect it to be in the $4,000 - $6,000 range to compete with the FS100. The C300 competes with the F3.
+1, just because it's 4k doesn't mean it's going to be absurdly expensive. Technology is getting cheaper by the day, and it's just a DSLR body with a different sensor. If you took a 1DX ($6800), removed the 12FPS, the AF system, and the mirror (in favor of evf) and swap the sensor. I mean a true video DSLR that all of the photography features are removed from. I just don't see what you could add to that camera to justify a $10k price tag. Absolutely no way it will be more than the C300 though, I'll bet anything on that.
I feel like the only reason they even previewed that camera at the C300 event was to appease the "little people" that were disappointed that the C300 was way out of their price range. I mean why show a product that early in development and take away the surprise from an official announcement?
I can believe I'm saying this but i agree with Axilrod

Remember that the 4K DSLR will not be a good stills camera as such.
Its resolution is 3840×2160 (8.3 million) pixels.
Thats what modern "4K" represents.
NOT 7680x4320 what you think would be 4K.
With this as the contributing factor they don't have to spend a crap tonne of money on Auto Focusing systems and other Photography features.
What I'm really hoping for is a 4K video DSLR that has dual "hot swap" CF cards (possibly a single SD for the stills also). In something that is similar to the 1D body but with a much better battery (even a slider tray that could take the LP-E6 batteries like on a 5D's BG-E6), Manual focusing like on the C300. All wrapped up for around the $4000 USD mark ($5k max).
Call it the 1D-C and i will be standing in line with my credit card in hand on the day of release.