For in-app purchase, when the final version of the game is out, it will likely looks something like this (NOT FINAL):
$1 gets you 80 event tickets
$5 gets you 500 event tickets
$10 gets you 1100 event tickets
$100 gets you 12500 event tickets
Under this scenario 10 event tickets would be valued at about a dime. Also, under this scenario, the backer $-worth of event tickets would be at the best ratio, so your $25 worth of event tickets would get you 3,125 tickets.
Again, all the above is NOT FINAL. :)