www.weaknees.com
$95 to format and install one or two new drives if you supply the drives. Possibly another $40 or so for brackets, a second fan, etc.
I was originally going to upgrade the TiVo myself, simply to get more recording time. You can download free Linux utilities to format the drives, which you have to plug into your desktop PC. Search "Hinsdale" and look for their how-to page. So I bought two WD 160GB drives - $160 x 2 but with $130 in rebates each for a net price of $30 x 2.
Then my PC died, and I'm not going to fix it, so I have to pay someone to do the upgrade. And WD/CompUSa are taking their sweet time sending me my rebate checks, so to date the darned drives have cost me the full $160 x 2. And the TiVo's original drive failed, so I [u]have[/to] get this done post-haste (the family is rebelling).
In short, I thought it would cost me $60 and some time, now it's costing me roughly $470 and only slightly less time. Not working to plan, this one.