View-Master
Original price: $12.50
Potential earnings: $430
The View-Master first came out in 1939, and the owners of these toys can make a few hundred off them now. This device was intended for children to view photographs of tourist sites such as Disneyland. Before smartphones were a thing, children brought them on Disneyland rides and other cool places. Then, of course, View-Masters got replaced by Smartphones, but those who still have it at home can sell it on eBay for $430.