Harry Potter and the Sorcerer's Stone
How we cite our quotes:
"If he wants ter go, a great Muggle like you won't stop him," growled Hagrid. "Stop Lily an' James Potter's son goin' ter Hogwarts! Yer mad. His name's been down ever since he was born." (4.130)
As far as we can tell, the question of who pays Harry's tuition is not fully addressed in this scene. Instead, it's quickly overshadowed by the idea that Harry's lineage demands he go to Hogwarts. In a way, the school itself is loyal to the children of its alumni, reserving places for them as soon as they come into existence.
Harry, who hadn't had any breakfast, leapt to his feet, but Ron's ears went pink again and he muttered that he'd brought sandwiches. Harry went out into the corridor. (6.163)
Although Ron is embarrassed by his family's poverty – they just don't have as much money as other old wizarding families – he's determined not to show it. Although his "ears [g]o pink" and he clearly feels unhappy about not being able to buy any snacks on the train, he defends his family and his situation by telling Harry that he's already got "sandwiches."
"Gryffindor," said Ron. Gloom seemed to be settling on him again. "Mom and Dad were in it, too. I don't know what they'll say if I'm not. I don't suppose Ravenclaw would be too bad, but imagine if they put me in Slytherin." (6.225)
Family loyalty works in reverse too when you're a Hogwarts kid – children of alumni feel an obligation to end up in the same house as their parents. The idea of not being in Gryffindor like his parents fills Ron with "gloom." He can't even "imagine" what they would do if he wasn't: "I don't know what they'll say if I'm not." While Ron seems unable to even countenance the idea of being a Slytherin, notice that he doesn't even mention Hufflepuff at all.