I dunno about dollar values of items posted on this particular forum's "found" section is. I suppose you could scroll down the past archives and simply do some column tabulations for year's worth of posts. But even then "value" is nebulous, because person's can give an appraised value, for example, of a 1 carot diamond ring. It might truthfully sell for $10k or $20k in the store, when it was new. So in the finder's mind, it is "worth" 10k or 20k, or whatever. But truth be told, the intrinsic scrap value of that ring (the stone when loose, and the melt value of the gold) might only be $5k.
Here's one that wasn't necessarily posted on T'net, but is worth mentioning, since you ask about value of things found. This was actually sold at auction, the year after the guy found it in the early 1980's. So there is no doubt as to the value. $45k was a LOT of money in 1983! Heck, you could probably still buy a house with that much money, in 1983, eh?

So it'd be (when factoring for inflation), like finding a ~ $100k object today?
In 1982, Jim Owens, from Seaside, CA, discovered a $5 "Schultz" coin while searching the beach near Monterey after a rough storm. The 1851 gold piece later sold for $45,000 at auction.