While I have no idea about the value of a Rebour drawing - they are not as rare as one might think. After all, Rebour was a professional artist, working 5 days a week cranking out these drawings. Whether it was ads, magazines, etc., almost all commissioned Rebour to draw for them.
Last spring, I saw three Rebour drawings, very similar to the one offered, of Herge bikes (not Herse, although similar and with many Herse parts). The asking price (nicely framed, but of course, I don't know whether acid-free matting, etc.) was about $ 160. As I was considering, I was informed that they had been bought by a Japanese collector...
That said, I probably will put a bid on the drawing offered on e-bay.
Jan Heine, Seattle