The closest thing to idiot proof instructions is the "quick guide" at
www.mfslive.org for the winmfs software.
This tells you how to copy the drive from a Series 3 or Tivo HD to a new virgin drive. It does not tell you how to remove the drive from the Tivo, etc, allthough in their quick guide for their bootable CD there are some instructions for hookup of the SATA drive to your PC motherboard.
I paid $99 for my 500GB Hitachi Deskstar drive which I then ran the acoustic management software on and installed in my Tivo HD. dvrupgrade.com wants $299 for a 500GB upgrade. So, it's more like triple the cost of doing it myself. DVRupgrade wants $599 for a 500GB Tivo HD. I paid $218 for my Tivo HD + $99 for the bigger HD. So in that case it's $300 more than doing it myself.