Yeah Dell's DP workstation options aren't cheap and I know what you are trying to show. Like $700 for 4GB of memory, the graphics card upgrade, dvd writer and the hard disk upgrade to bring it similar to the Mac Pro and the higher cost for 2.66GHz and 2.93GHz options make them seem expensive.
The Dell systems benefit from comming with the minimum specs though. So you can use cheaper 3rd party options. 12GB of ECC memory can be had for $300, or $550 for 3x4GB DIMMS. Hard disks are way, way cheaper even for enterpise grade ones and you can add consumer graphics to match the Mac Pro for $70 (GT120) or $160 (4870).