You're probably right on all counts, the server/workstation cpus will be more expensive than current ones (at similar clocks) and the dual-quad 2.66GHz nehalem Mac Pro will probably cost $2999. But it doesn't negate the fact that this Mac will probably be faster than the current dual-quad 3.0 that ships for $3599.
The other thing is that it makes no sense what so ever to ship a single cpu model on a dual-cpu motherboard with the changes in the architecture. So, will Apple release two versions of the Mac Pro? Single cpu (X58 chipset and Core i7 cpu) and dual cpu (Tylersburg-EP and two xeon nehalems)...
Given the low price of the high-end desktop cpus (Core i7 965/940/920), Apple COULD release a single cpu Mac Pro for about $1299 (the quad 2.66GHz core i7 920 will cost about $284, the 2.93GHz $562, and the 3.20GHz $999).
Power requierements: a single Core i7 has a TDP of 130W, dual xeon nehalems cpus have a combined TDP of 190W or 260W for the dual 3.20GHz cpus. With each revisions of the Mac Pro the TDP increases. Maybe it's time to cool down a little.
So, here are my wishes (or better, the possibilities) for two lines of Mac Pro:
Uni-processor Mac Pro (X58 chipset, Core i7 cpus):
$1299 quad 2.66GHz, 3GB RAM, 320GB HDD, Superdrive, nvidia GPU
$1599 quad 2.93GHz, 3GB RAM, 320GB HDD, Superdrive, nvidia GPU
$1999 quad 3.20GHz, 3GB RAM, 320GB HDD, Superdrive, nvidia GPU
Wishful thinking, Apple would probably sell those for $1599/1999/2499 (if not higher), still I'd buy one or two of them...
Dual-processor Mac Pro (Tylersburg-EP chipset, nehalem Xeon cpus):
$2999 dual-quad 2.66GHz, 3GB RAM, 320GB HDD, Superdrive, nvidia GPU (the cpus X5560 will cost $958 each)
$3999 dual-quad 2.93GHz, 3GB RAM, 320GB HDD, Superdrive, nvidia GPU (the cpus X5570 will cost $1,386 each)
$4599 dual-quad 3.20GHz, 3GB RAM, 320GB HDD, Superdrive, nvidia GPU (the cpus W5580 will cost $1,600 each)