Difficult question.
I'd guess that it's like many high demand events:
Early: expensive, due to desire to lock things in for both sellers and buyers.
Middle: somewhat cheaper, sellers starting to worry about their profit, buyers more "let's see what I can get"
Late: most expensive, driven by buyers at the "I promised someone we'd go" stage or even at the "I already sold this to someone" stage
Very late: their may be bargains, but wow, congrats.
For buyers, the hard part is trying go get in at that middle stage.
What are you willing to pay?
(Just kidding, my maybe extra tickets are not yet for sale. Still figuring out family + friends plans.)
Edit to add that the usual cycle is also messed up more than usual by school ties. If a classmate I barely know is looking for tickets, they'll get priority from me. They're still not getting face value, of course, basic economics)