The economics of this are kind of fascinating.
There surely are more diehard ND fans willing to pay up than there are IU fans. But some will save their bullets for the second round, which will be easier to make the travel work, being three weeks away in a much larger city with more hotel rooms and flights. It is also a holiday week whereas this game will take place on what is a workday for most people.
Meantime, for Indiana fans this is a once-in-a-lifetime sort of event, and many won't even need hotel rooms or airbnbs (which have soared in price) because they live close enough to drive, which is not the case for most of ND's fan base. There may be far more ND fans nationally, but there are probably more IU alums who live within, say, a three hour drive, just given the size of the schools.
As for ticket prices, they will go down in price starting tomorrow when tens of thousands of alums get tickets in the lottery, some of which they will not be able to use. But how much?
Some enterprising economics grad student should study this closely.