I got an extra FI controller with my wife's Vanagon  My mechanic says
that these are unavailable, and needs one to finish fixing another
customers drive.   He said that he would pay me for it, but I have no
clue what the going price is for one.

What should I charge him?  BTW: he is my favorite mechanic, and has
done me a TON of favors so I don't want to stiff him.

-Gary