if you are a financial strapped groomsman are you required to buy a gift

My son was asked to be a groomsman in a wedding of a close friend. he is paying for the tux rental and also had to pay for cowboy boots, as that is what the bride and groom wanted. unfortunately size 14 boots don't come cheap! my son is a single father with two boys who, although is employed, is struggling to keep his head above water. he commented he was going to use a credit card to get them a $100 gift. I told him that seemed extreme considering his situation. He recently asked me to look at his budget and see if I could help him cut back his expenses so I know he's really concerned about his situation. Is he required to buy the bride and groom a gift. They are fully aware of his situation.