There are some mages who charge for the use of their portal service. You probably won't make very much money off of it, but you might make some. Travel by other means is fairly cheap and has advantages of its own (looking at the landscape while onboard a flying creature is awesome!).
EDIT: In the last patch they added a reagent cost to the use of Teleportation. It seems to me, then, that a mage will be very reluctant to use this ability on anyone besides himself unless he is sufficiently rewarded-- in which case, the potential customer will probably seek alternate modes of transport. Too bad.
Edited, Mon Nov 8 13:52:59 2004 by ChahDresh