Well, my character went on some task for Eliath... and one hobgoblin, one 8-headed hydra, four leucrotta, six orcs, eight gnolls, and two bugbears later I found my way out of Undermountain with way more than enough treasure to pay for that stupid divination spell and have a a sizeable sum left over to, oh I don't know, buy a ship or a castle or something.
The funny thing is, the first thing I did was return Eliath his cases as promised.
For a paltry sum of 1,200 gp.
Which is not even worth one of the gems I found.
ha ha ha. ha. what a knee slapper.
By the way, the 2nd ed. Undermountain book, page 61. That's where the jackpot is. Just don't bother with pile 3, it has nothing but non-magical weapons in it.
Oh, and the Ivory tusks are only worth 20 gp each. So don't stress over trying to figure out how to carry them out.