I saw this topic earlier today and have been trying to come up with something
I've spent a large amount of money on. Nothing initially sprung though.
Many years ago, in the early 90's, there was a card shop in Novi that had a pack of 1989-90 NBA Hoops cards sitting in a display case. The packaging was made out of that semi-transparent plastic that made it possible to see the first card of the pack if you looked closely enough. On top of this particular pack was a true David Robinson rookie card. Since it clearly contained the Robinson gem, this pack was being sold for $25 or $30. I knew I'd never be able to afford it. But for my birthday later that year ....
So I guess I didn't shell out the money myself, but that's probably the most I've spent by proxy. I debated for a while whether I should open the pack too. Being an impulsive youngster, I busted that thing open and never looked back.
Most recently, I spent $10 (which felt like a lot at the time) to buy a random mass of basketball cards at a garage sale. The man's brother-in-law owned a card shop in Chicago but had just passed away. As such, he was looking to rid of inventory. The cards I bought included a treasure trove of rare Michael Jordan "comeback" cards alongside a fair chunk of Spanish language Jordans. They all turned out to be worth a buck or two a piece. However, a Topps Finest refractor was also part of the deal, and at one point I've read that might be worth over $100. So that worked out.