I recently bought 3x iP4000 and 1x iP4200 printheads from this ebay shop after some private feedback from someone else on this forum who tried them out.
http://www.inkcessories.com/ $49.95 for the ip4000 printhead. I just bought an i960 printhead. Good service and prompt delivery. precision roller was much higher for the i960 than inkcessories.