Billy gave the money he earned from the raccoon hides to his father. This was a lot of money, too, since "the price of coonskins jumped sky-high" do to demand in the East for coonskin coats. Each hide was worth from four to ten dollars.
Billy didn't really care about the money, though. He never asked his father about it and simply figured the money was being saved for something. As he says in chapter ten, "I wasn't bothered by it and I asked no questions." Instead, Billy was fixated on his dogs, who were his constant companions.
Billy's attitude towards money is one of the themes of the book. He works very hard to save the fifty dollars he needs to buy the dogs, but the money has little meaning to him beyond that. Similarly, even though the dogs provide him with the means to get many coonskins, he is more interested in the dogs and the adventure of hunting than he is in the money he earns doing it.