My cousin got married last year. Guests could attend the ceremony for free, but for the reception afterwards they asked guests to pay $10 each, to help cover the cost of the buffet. The money they got from guests for the reception covered a little under half of the cost of the food and drink provided. Most people paid (I was maid of honor so I didn't have to, nor did the best man) but even those who didn't pay were welcome at the buffet/bar. The money they asked for was just to help cover the cost, it didn't pay for the entire wedding (or even the entire buffet) but without everyone's contributions it would of been an alcohol free reception. No one minded, and almost everyone chucked in their ten bucks.
It was a good day, I look horrible in every photo taken but ultimately it was fun.