eBay is usually the cheapest IMO
The same vintage "rare" McDonald's T-shirt I wanted was $50+ on Etsy, Mercari, Poshmark, even some eBay sellers. But I got it for $2 from a dude on eBay ๐คทโโ๏ธ
Etsy is way worse at what OP is talking about, but I'm using it for vintage stuff not really electronics. For electronic stuff I use Swappa mostly
Its some shirt they gave out as a promotion for the Flintstones movie in 1994 lol. I have weird taste