What should the best man pay at a wedding?

The best man should pay for all of his own expenses. Brides, grooms and possibly their parents are paying for the wedding and they are not responsible for the expenses (travel, clothes, accommodations, meals) incurred by any wedding guest including the best man. When you are invited to a wedding and asked to be a part of someone's bridal party; it is an honor. You don't beg the bride and groom to buy you clothes, pay for your hotel room, etc. If you can't afford any of these things then ask if you can wear a suit that you already have insteading of buying or renting one, take the bus to the wedding city instead of flying and stay with friends or family instead of in a hotel when you get there. Find less expensive ways to still be in the bridal party. If the couple makes outrageous demands like requesting the bridal party to take a week off of work to stay in an expensive resort for a wedding in Another Country; then you can just say that you are flattered that your friend wants you to be his best man but that you cannot afford everything that goes along with it.