The thing is $550 is not unreasonable from a niche marketing perspective. I manufacture and sell a bracket system to convert 1968-1982 Corvettes from vacuum to electric. It runs as much as $750 to buy all new GM headlight actuators, electronic, and my brackets. From what I can gauge looking at his stuff his profit margin is razor thin at $550.
I do think however you could do this yourself for a bit less using a
www.uslinear.com actuator and some creative thought. However, these actuators often go as much as $200 each, so you are right back in the same price range.