He goes to the plane that day, happily gives up his overbooked seat, gets a free flight anywhere in the country for being so reasonable, and uses his exchangable ticket on a flight he will use later in the year. If necessary, use compassion fares. Airlines offer discounted bereavement fares if you can show proof of death and explain your relationship to the deceased. Once you get to your destination, you can save even more money. Traveling by bus or subway saves money, and if you will be there for awhile, consider getting a bus pass.
Lodging can be very expensive or very cheap.
If you are going to travel overseas, you can exchange homes with a family in the country you are going to. You can rent an apartment instead of staying in a hotel. You can stay in a discount motel instead of a hotel. You can stay in a college dorm instead of a motel. You can camp.