I just bought a voltage regulator les than a month ago from O'reilys. It was ~$35 after tax and has that limited lifetime warranty. I have since switched to a 200sx alternator due to my 35amp dying on me, but I don't think that was related to the voltage regulator. I had a coolant leak above the alt from the lower water neck and the 35amp was pretty well gunked up.
One thing about the O'reily VR, it has a board on the bottem where it mounts to the firewall with a long spring peice. This spring quickly heats up and burns the board, causing some smoke. Both the old VR and the new VR burned in the same pattern, so these may not be quality parts.