Yup those big air horns always bring in big money on ebay the truckers love em.
Some of the older trucks sport air horns with the longer tumpet, these always sell on ebay for $100.00 or more. Steam whistles are always a good find, last one I found stood 4 ft high offered $500.00 and still no sale.
Not far from me ther's are two old locomotoves sitting on display and both have their air horns, I'm curious how no one has yet stolen them as both are failry isolated.
Over the years it has been proven time and again there is no shortage of this junk to consider it rare.