I dont see where the problem is with the most RAW like method of Nadaka option 2:
You find a briefcase full of cash.
It has a PDC(x) set to it: how much it would cost to get a briefcase full of cash.
If your character purchased that PDC(x) briefcase he Wealth would go down according to purchase rules.
But you are not purchasing it, you are selling that PDC(x) item to recover Wealth, and the amount of Wealth you recover would be the amount of Wealth you would lose to purchase it.
Look at it this way
The PDC(14) CashBag wouldnt raise the wealth of the Wealth15 guy that found it,
mainly because the Wealth15 guy that found it can repeatedly just make that bag appear without losing wealth doing so... he has an unlimited suply of PDC14 CashBags he can have. Now that he found this one, he has an Unlimited Suply and one more.
Due to the base concept of the Wealth system,
Mr Wealth15 can just "buy" as many PDC14 Cashbags as he wants.
Finding one more is no big deal.
Jimmy goes to the stip club with his Wealth 4,
and can shove as many PDC1 Bills in the girls thong as he wants,
"buying" a PDC1 Bill will not lower his wealth, time after time, all night long.
If he finds a PDC1 Bill on the gound, it wont help his Wealth one bit, because he already has an unlimited supply of PDC1 Bills
"Bring me a beer every 10 minutes Cindi, and keep a Fivespot for yourself,
I'm gonna Take10 these purchases all night long"