When have I not overpaid 
But as mentioned by @bash2112:
Almost everything I overpaid for years ago are worth a lot more nowadays anyway.
But, to give one example I’ve given loads of times before:
The Pikachu with YOU Wagon promo.
To give the short summary this time: released in 2014. None available for sale until Dec. 2016 when one popped up for auction, which ended at 135,000 Japanese Yen (~1.2k USD at the time) and I lost. Few more popped up, and I placed a bid of 777,777 Japanese Yen on one auction, which I ended up winning for 777,000 (950 USD incl. all middleman/shipping/import fees). 
While that auction was active, there were BINs available for ~600,000. In halve a year, it dropped to ~100-125 USD in price, and it remained <250 for a couple years. But nowadays it’s above 1.5k, so 
Looking back on when I first posted about that bad deal, I also see I wrote this:
Funny to look back at the days pre-orders could drop in price after their release, instead of going 10x MSRP and being bought out by bots/scalpers. 
Greetz,
Quuador