Poverty seems to be everywhere in the American that Sal sees. He meets homeless men on the side of the road and musicians playing for money. Sal even experiences poverty first hand as he travels. As for poor money management, Sal and his friends display an inability to find any sort of middle ground. Sal is either sending money home to his aunt or asking her for more money.
Sal and Dean differ in many ways, but the one thing they have in common is their constant state of poverty. Poverty is a lens through which we can view their friendship.