Greenlanders rather than Danes may be the deciding party.
The Danish annual support is a fixed amount. This amount may be10% of what they spend on defense / aid, but a far smaller percent of the US budget (i.e., we would spend nowhere close to 10% of OUR budget).
A bargain if we can …
I seriously doubt if anything will come of this beyond a few good laughs.
On the other hand, I'm certain that Pres. Trump is thinking very strategically, and such thinking may well help in our rivalry with the New Russian Empire.