The airport's official website quotes �43.70.
http://www.aena.es/csee/Satellite?cid=10488589 22698&pagename=Estandar%2FPage%2FAeropuerto&SM O=1&SiteName=MAH&p=1048858922686&c=Page&MO=1
This site seems to agree with that sort of figure. (it suggests around �45):
http://www.islas.co.uk/ciutadella.htm
Cala en Bosch is 10km past Ciutadella, so the fare will be slightly higher.
If, during your stay, you need to travel between Ciutadella and Cala en Bosch, buses run every 15 minutes from Monday to Saturday and every half hour on Sundays:
http://php.infotelecom.es/autocarestorres/prec ios.php?hor=ver&lang=uk
Chris