Mdthbs

In Harry's first year on the train to Hogwarts, Ron doesn't have the money to buy something when the woman with the cart comes.

Ron’s ears went pink again and he muttered that he’d brought sand­wiches.

Harry bought, among other things, some Chocolate Frogs.

What are these?” Harry asked Ron, holding up a pack of Chocolate Frogs. ...

“Oh, of course, you wouldn’t know — Chocolate Frogs have cards inside them, you know, to collect — famous witches and wizards. I’ve got about five hundred, but I haven’t got Agrippa or Ptolemy.”

How did Ron get five hundred cards? Where did he get the money for them? Sweets with cards probably cost more than sweets without cards, and Ron doesn't have the money to buy any sweets.

This is a picture of my fridge's door:

As you can guess, I collect department/counties magnets. I have been for four years. They come from a special brand of ham and cheese escalope, there's one magnet per pack of two escalopes. Now I will admit I eat a LOT of those "cordon bleus", but I also happen to have friends who know about my life goal to complete the map of France in magnets, and occasionally give me some.

The same could have happened to Ron. Friends, siblings, siblings's friends who know about his collection - probably a bunch were granted to him.

_{For the record, my freezer door has the remaining duplicate magnets.}

I can't remember, it's quite a while. But I don't think this has ever been addressed. So, an educated guess: he had two older brothers. They might've lost interest in the cards they had and given them to Ron. With the Weasleys, everything is handed down.

Also, everything is shared. So, it might be that not he has 500 of these cards but they, as the brohter Fred, George and Ron, do have 500.

We see evidence elsewhere that people give cards to each other, presumably when they themselves don’t collect them or when they already have a particular card. From Chapter Thirteen of Philosopher’s Stone:

Neville’s lips twitched in a weak smile as he unwrapped the frog.

“Thanks, Harry . . . I think I’ll go to bed. . . . D’you want the card, you collect them, don’t you?”

It would thus seem eminently reasonable that Ron acquired much of his collection without having to buy any frogs. If you hang out with enough other people who don’t care for the cards, or who already have a big collection, it shouldn’t be too difficult to amass a few hundred cards without paying for them.

His parents bought them.

Ron's family isn't wealthy in the way that the Malfoys or even the Potters are. But his parents aren't broke. They have enough money to afford small luxuries, such as chocolate with collectable cards for their youngest son.

However they are too frugal to send Ron to school with a pocketful of galleons. Ron doesn't have money on the train to buy sweets. But no doubt he nagged his parents for chocolate frogs every time they went shopping. Molly and Arthur have plenty enough money to afford a sickle to appease their 10-year-old. His claim of "500" should be treated with some scepticism. Boys tend to exaggerate such things in order to impress others.