[Porsche-O-Phile]

Mostly the value is for uncirculated. The same bill found in a cash register somewhere (even if it's in good shape) would be worth what - maybe a hundred bucks?

Collecting circulated stuff is a lot easier/simpler but the values tend to be absurdly lower. When you get into uncirculated items, it's more like collecting artwork than money - the stuff is printed/packaged with the intention of never being spent. It's not really "money" per se at that point, at least that's how I see it.