IO540
I fear that you over estimate the quality of avionics instalations, most installers don't include the avionics fan in the cost of a new avionics fit for fear of being undercut on the price by another installer.
It is only the wise owner who knows that the avionics fan will save £££££££££ over the years and those without the wisdom save £150 on the new avionic fit and pay & pay later!