The Bentley Compu-Vision. Had it been released in 1976, it would've been state-of-the-art, albeit in with a sea of other Pong clones, getting ready to trigger the first video game crash. However, Bentley (whoever the hell they were; apparently no connection whatsoever to the car company) decided to release it in 1983, just as the video game market was getting ready to crash again. According to this page, it sold for $25 new (equivalent to $64 today), which probably made it the cheapest console on the market, though I reckon it was still overpriced..........
-Adam