From the beginning of the Harry Potter series, the Weasley family's money problems come up repeatedly. Ron has to get all of his textbooks used, he is afraid to ask his parents to spend money on a new wand, and he doesn't even have enough spending money to buy a snack on the Hogwarts train. During the summer before Ron's third year, Mr. Weasley does win the Daily Prophet draw, but apparently he uses all, or nearly all, the money before the summer is out:
I couldn't believe it when Dad won the Daily Prophet draw. Seven hundred Galleons! Most of it's gone on this trip, but they're going to buy me a new wand for next year.
But when Ron returns to Hogwarts for his third year, he is able to spend money rather freely on his trips to Hogsmeade. With the prize money gone, how were Ron and his parents able to afford it?