how about this system?
you can pay to be transported via ship/horse carriage/transport etc, from city to city.
but you also can set a Waypoint at where you currently are, and fasttravel to this waypoint from anywhere you want, and back to your position you fast traveled (but only from the waypoint).
this way, it costs something if you want to go somewhere, and you have to plan ahead with the waypoint if you want to return. the waypoint could be a magic item you get for a quest.
Yeah this sounds better than OP's way of doing it. OP's way is good too though.
Still, the problem according to me does not lie in the "temptation" to use fast travel. The problem lies that Oblivion's way of fast travel has no explanation and does not have any restrictions, both of which a good travel system should have in my opinion.
Your (OP) idea restricts fast travel. Good.
But it still doesn't explain fast travel, more than clicking on the map and says "want to fast travel to...?". Therefore, I think Darktimes proposal is a bit better. It gives you an explanation. A magic item is an explanation. A spell could also be one.
Moreover, transportation systems is an excellent explanation with restrictions. Transportation systems is very logical to exist in a world like TES (and in our own world...), and they have done so before.
The best way is therefore to only follow Morrowind's transportation system idea, but because there are people who like to fast travel (as in not using travel services), an idea with waypoints or teleportation spells could also be good.
It would kind of be like a reversed mark/recall spell. You mark the place you want to go to, then teleport to get there. Of course, a normal mark/recall spell would be very suitable as well.