Thx alot Von Kurst. Its so true that they are nothing more than a big sink to GC.
Indeed, I think a good compromise would be to add the value of the two horses (so 6) for the Stage coach. and add 12 for the engine of chaos ( for the demon that clearly worths twice the horses).
However, On most engine of chaos I saw here, the demon was ''hidden''. Personnaly, my plans for my future engine looks more like a techno-geared-coach pulled by a huge flaming ''Taurus'' demon. Still, it's a personal taste I guess.