TiVoLovers is reporting that Dell has a promotion on their products that lets you get a Series3 TiVo for only $510.98 after rebates and discounts. $500ish seems like the price the S3 should have been.
Also worth noting: I tossed up a review of the Weaknees upgrade drive for the Series 3 TiVo. Weaknees sent me a 750Gb drive a few weeks ago and I've been happily enjoying it ever since. Of course it is an expensive add-on to a fairly expensive product, but it does triple your capacity.