Just FYI,
Besthesda wanted to charge me $10, just for a new paper map...
So, I'm guessing that a construction set CD would be at least $15 to $20, if not more. You may want to consider just buying a complete GOTY edition of Morrowind; they can be obtained quite cheaply these days.
Moreover, some of the best mods out there require the expansions, because of new scripting features, textures etc.