My treasure hunting was confined to estate sales, tag sales, and flea markets. Mostly it was finding things I really wanted but couldn't afford retail. There's a few things that stand out:

A deep sea diver's watch my son bought for $2 at a tag sale that retailed around $300

A winter coat I paid $3 for at a tag sale and have worn for 20+ years. I get a lot of complements on it still, it's still in really good shape.

Something like 9 rolls of wire garden fencing and 2 gates for $80. It would have retailed at about $40/roll. This enabled us to build the layer pen initially and was also used to re-fence the Small garden. I'm still using it for various things, lastly for fencing for the little trees.

Yeah, finding treasures is fun, especially when they are really cheap!