Answer:
We learn that Dexter's family is not old money. His father owns only the "second best" grocery store in a small resort town in Minnesota—and it is not the grocery the rich people patronize. We learn that Dexter's mother is a lower-class Eastern European (Czech) immigrant, which at least suggests that his father comes from a similar background:
His mother’s name had been Krimslich. She was a Bohemian of the peasant class and she had talked broken English to the end of her days.
Dexter may not absolutely need the $30 a month he earns as a caddy, but when he decides to quit:
The enormity of his decision frightened him. He was a favorite caddy, and the thirty dollars a month he earned through the summer were not to be made elsewhere around the lake.
His father is prosperous enough to send him to the state university, but Dexter goes to the more expensive prestigious East Coast school. How he pays the difference, we don't know, but we later learn he couldn't afford..
Explanation:
