Like the first poster said, it depends on who is still in it, but that's more for scalpers. So say KSU makes it to the second round, scalpers love it because there's a big fan base there that will be buying up tickets to that next game. KSU lost the wednesday night game last year so Thursday morning there were tickets for sale everywhere when I was trying to dump my tickets for the early Thursday games. That's good news for anyone trying to find a ticket.
I had all of my tickets pre-purchased but had plenty of friends buying tickets around P&L that ended up with better seats than I had for the same price or less. You shouldn't have a problem finding tickets at prices less than face value on the first day, and depending on if they advance and who they would play on Friday. There's all sorts of black dudes with blu tooth scalping tickets in the P&L district. I would suggest venturing down one of the side streets (still around P&L) and try to find someone who doesn't have 200+ tickets they're trying to sell and see if you can find a better deal. Otherwise just try to haggle with one of the 'professional' scalpers close to game time because they'll be trying to get rid of them. I got mine in advance because I wasn't sure how the scalping was down there but really, if I go down again that's probably the route I'll go because you can end up with some pretty great seats for a reasonable price if you aren't totally naive. Good luck!
Edit: the face value for my championship tickets were $100. Now, it was a KU/ISU matchup (a scalpers wet dream) so tickets were going for $250-300 easily outside the arena, so I saved a lot of money there. I thought I either get to watch the clones battle for a big XII championship, or make upwards of $300 off of two tickets so I was making out well either way.