Are there any other, either creatures or human, places that will pay for some of the more expensive items in the game? I am already aware of the drunken mud crab and the bongo playing scamp but are there any others in the morrowind game excluding the expansions?

Thanks in advance
RaS

Creeper in Caldera.
I could tell you where to find him, but don't want to spoil the fun - it's not difficult (but he's not among the shop-keepers of Caldera).

Creeper is the scamp he mentioned.

But other than those two, Nalcarya in Balmyra is one of the merchants with a lot of money (or rather, valuable items to trade for goods).

I never saw Creeper playing bongos. :-)
I just loaded an old save game and visited Creeper. There are "bongos" on a shelf behind Creeper indeed, but does he actually them (ingame)?

There's a great little mod that makes him do just that. "Creeper the Drummer"
http://www.nexusmods.com/morrowind/mods/42451/?

It's very easy to give Creeper more money. Even a complete novice like me managed to do it when the game first came out.
Open the Morrowind TES construction set (TES Construction Set.exe located in the Morrowind folder)
Click open folder to bring up the data files and check the first box called Morrowind.esm.
Wait ages for everything to load
Then, in the object window, click the tab "Creature". You can sort the very long list by name (3rd column) and find Creeper. Double click on this line to bring up a box of Creeper's properties. At the bottom of the box are 3 buttons, "Dialogue", "Animation" and "AI". Click AI
This brings up AI Data - Scamp_creeper
Click the tab "Services" where you will see that Creeper's Barter gold is 5000. Change this to whatever you want. I gave Creeper 500,00 gold.

Then save and as you exit TES construction Set it will ask if you want to save changes. It will also ask you to give the save a name. I called mine "RichCreeper".

Now load the game but before you start to play, click "Data" files and find you saved TES file. Mine is called "RichCreeper" Yours will be whatever you called the TES Construction Set save. Make sure that box is checked. Now start your game and you will find that Creeper has as gold as you gave him.

Yes, you are certainly right - you can do (almost) everything with the Construction Set.

We were discussing in-game solutions, without using mods (your RichCreeper file is a mod - nothing wrong with that).
It is a Morrowind experience I guess we all made after we had gained a couple of levels that it's quite difficult (or impossible) to convert loot to cash in this game.
Which of course leads to a second question: What's the point of collecting all that loot or it's cash equivalent, except for the sake of collecting? :-)