Actually, the price difference is pretty big. You can get the Geforce SDR for about $130, while the DDR is a bit over $200. $70 (about 55% more than the SDR) is nothing to sneeze at. You won't be playing at super high resolutions or running FSAA, but it is certainly a good card.
The SDR is the bargain of a lifetime when compared to everything else below $200. Once you get near $200, the DDR is the bargain of a lifetime, beating out everything until you get to the $300 GF2 and Voodoo 5. Even then the GF DDR beats out the V5 when paired with a <650mhz (maybe more) CPU.
Is it worth the extra $70? Thats a very tough choice. I think spending $70 getting DDR instead of SDR would be better than spending $70 on some other computer upgrade.
BP6, Celermine 566@850, 320meg, CL TNT2U 175/220
BP6, P3-700@770 (for now), 320mb, eVGA MX Plus (dual CRT), waiting for VIVO module