Your estimates are too high, I just pointed my Dad to a Samsung laptop on sale at Best Buy for $300 shipped last weekend. 2.7Ghz AMD A6, 4GB RAM, 500GB drive which would be plenty for a basic DVR (500GB is what basic Tivos ship with now). Add in a SiliconDust Cablecard tuner which is routinely on sale for around $130 and a $20 USB remote/receiver kit and you're set for about $450. Not bad, but also not a Tivo - there are pros and cons to both.
Since it already has Windows 8 Basic ("Core") installed, you'll also need to upgrade to Pro, if you want to be able to install WMC - which is $70 through tomorrow, and $100 thereafter (for the "Pro Pack with Media Center" upgrade).
Those less-expensive upgrade deals they've had going are only for upgrading from pre-Windows 8 versions. I found that out the hard way myself, when I thought I was getting a great deal (an HP with the same specs as that Samsung, for $329).
I haven't noticed any store models for sale with Pro pre-installed as of yet. Maybe they'll release some that way eventually, but I expect them to be priced accordingly.
So, people, be forewarned.
Edited by Rammitinski - 1/30/13 at 11:37pm