I usually park at a downtown ramp and walk. That's about $5 for a Saturday. You can find really great parking on Craig's List which will put you in the lots that come with season tickets requiring a donation. A friend's season tickets include a spot by the Stock Pavilion, which is nice because he's guaranteed a spot, but it's still a pretty good walk. Last year, my son and I parked on a street near Hilldale (about halfway in for us) and biked the rest of the way, which was pretty slick, although biking near Camp Randall prior to kickoff and after the game can be harrowing.
I like to kick around downtown after the game, so I have never looked into shuttle buses run by bars around town. But that seems like a pretty good option if you don't mind getting out right after the game. Most of the big sports bars have them (Babe's, Pooley's).