I got my D&D Basic box set from a charity shop, £2.50. There's one going for over £150 on ebay right now. Got my Baldur's Gate box set from a charity shop too for £2.50. I also got Flash 4 (I think) for a couple of quid, it was selling second hand on amazon for about £200, but I was an anxious, clueless kid and was too scared to sell it.
Yesterday I got some squishmallows for my niece at £1 each. We still get good stuff here.
Even here, some like Oxfam will save the more valuable stuff to sell on ebay. I worked at two charity shops back in my twenties, so I got to the good stuff first haha. The Baldur's Gate was lucky because another customer was going to buy it for her son, but changed her mind when she saw the age rating, and I was like, bagsy this!