Real Atari Pongs have value and some of the assorted stand up clones do as well. Particularly if they were made by a company that survived into the classic era, Williams, Midway, Taito, Sega, etc all had Pong clones as their first video games, and some collectors want those, particularly those that collect a certain company.
However off brand 4-player tables. Not much demand, probably 100 different companies made them and they take up a ton of space.