The RAM, VRAM and Flash chips, the PCIe SSD-controller chip, the wireless chips and the GPUs are manufactured outside the US by Samsung's and TSMC's fabs in Korea and Taiwan. All of Intel's stuff are manufactured and designed in the US. I see no reason why manufacturing and packaging of everything else wouldn't be made in the US too, and if they are highly automated then there'd be no more expensive than if it were manufactured outside of the US.
When it comes to price, I think that most estimates are vastly exaggerated. The Xeon Ivy Bridge E5 V2 processor, won't be more expensive than the ones that is in the current model, and the list price of them is around $1500 dollars. The list price of a Radeon HD 7990 is $1000. 32 GB of 1866 GHz DDR3 RAM cost $300. 512 GB of FusionIO-SSDs are $2000. It's be absurd to think that Apple would pay list price for those components so why this computer would cost $6000 I can't understand. A off the shelf PC, built to match the specs would, but I think Apple will undercut the list price by something like a half. The new Mac Pro would, even if it is a "flop" generate volumes AMD and FusionIO would only dream of. So.. $3000. That's my guess.