The lowest reasonably future-proofed prosumer Mac Pro I can price out is just a shade over $3k with sales tax with the educational discount.
2GB of RAM (since OWC is the only third-party available currently, and they're actually higher), x1900XT, 160GB HD, Bluetooth/Wireless, 2.66 (looking at benchmarks for the 2.0 vs. 2.66, the difference is noticeable and should only get larger over time), one drive, etc.. Once you actually take advantage of the Mac Pro's space (two hard drives, another superdrive or Blu-Ray drive whenever, extra RAM), you're talking about a $4000+ computer.
At that kind of price target, Apple has to sell something more reasonable - a $1500-1800 mid-range desktop (Conroe based) with more expandability or at least a Conroe iMac with two HDs.