On my Quickie Q2 I am in the midst of removing my automotive belt-driven alternator from the front and installing a B&C gear-driven alternator that connects to the engine in the rear. The B&C gear-driven alternator is just shy of $700, but the real kicker is that I need to send them a gear assembly which I don't have. These 5 little parts brand new from Continental/Aircraft Spruce are $1,100, which would bring my total to $1,800.
So now I'm scouring the salvage companies trying to get a refurbished set of parts.
I can also appreciate why people put automotive alternators on these engines!