It looks like some of the long lost ET game cartridges have been found ...
https://www.youtube.com/watch?v=pGbLENif_eI
https://www.youtube.com/watch?v=pGbLENif_eI
It's a bit hard to know when a market will implode. Atari was selling carts in the millions before the bust, they just went crazy with bad games and got stuck with them.