I got a used Maxtor 80GB disk from Ebay for £4.99 + (£3.20 P&P) for my TiVo messing around.
Worked out a really handy I was recently given a TiVo with lifetime subscription that had suffered a lightning strike so had a duff modem. So restored an image onto my Ebay 80GB drive, added cachecard drivers, renamed the modemtest executable, plugged in my cachecard and the TiVo booted and accessed the network fine. So a free TiVo (excluding needing to buy a bigger disk, a new PSU, a cachecard and a DTT box.....but maybe one day....or just spare motherboard for current TiVo...).