The budget to pay for these finds is regularly exceeded already. Paying the gold price would fleece the National Museum.
Understood. But it's also true that you get what you pay for.
Getting a cut is probably better.
Spending gold you can't document the origin of is most decidedly going to be a hassle. Certainly not without risk. And you probably don't have money laundering connections.
And you'll sleep better at night.
In this case it bought the most productive amateur archeology community in Europe :)