There is a Banknote collectables market, and like any collectables market there are the rarities, varieties, theme collectors, serial number collectors, Replacement note collectors and error note collectors. I've done some Serial number hunting and got lucky finding a special serial number as an example, 1234567 and sell it on Ebay at a premium well above face value. OF the few Collector shows I've been, it still boggles my mind what some collectors will pay for a special numbered banknote. A cousin of mine did this for a while and did well looking for Replacement notes until the market became oversaturated of them.
Otherwise, they make great inexpensive backgrounds for my silver coin photography.
