This is typical in our area as well.
I'm from Wisconsin also. For a casual acquaintance - $25 is my norm. My DD is in high school, so am starting to get multiple invites for graduation parties.
I coach a high school team, and when my seniors graduate, they will also get $25.
If the graduate was closer to the family - i.e. maybe the would babysit, etc. I would give more.

