Pricing ranges from $3000 for the smallest configuration (3.7GHz quad-core CPU, 12GB DDR3 ECC RAM, 256GB SSD, dual AMD FirePro D300 GPUs with 2GB GDDR5 VRAM) up to a whopping $9600 for the maxed-out configuration (2.7GHz 12-core CPU, 64GB DDR3 ECC RAM, 1TB SSD, dual AMD FirePro D700 GPUs with 6GB GDDR5 VRAM). An AppleCare 3-year extended warranty adds $250.
Expensive? You bet. Do I want one? Oh yeah! I don't do anything today that requires this kind of power, but if a unit like this is well constructed, it is likely that it will have an operational lifespan of 7-10 years (not counting the need to replace the SSD, which probably won't last that long.)
Interestingly, the price for the basic configuration is about the same as what I paid for my first Mac (a 2002 PowerMac G4 with dual 1GBz PowerPC CPUs). Add on an external 4TB hard drive (e.g. an enterprise-class hard drive combined with a USB3 enclosure for under $250) and you've got a great system, for about the usual price you'd pay for a high-end desktop from any vendor at any time.