The best men and groomsmen usually pay for the bachelor party (activities, entertainment, drinks, meals, party rental, etc.)
There are some exceptions when the groom contributes to the expenses; for example, if the party is out of town, but most of the time, the guest of honor does not pay.
Guys, you're throwing this single send-off party for your best friend, who will soon be married. Prepare your wallets and make the celebration memorable!