Released on the Super Famicom, the game sees you assuming the role of the titular merchant from the fourth mainline Dragon Quest adventure. While it was a success in Japan, it never got a Western localisation – however, as noted by Games Radar, an old interview with Nintendo Age's eZine reveals that former Nintendo game counsellor Tom Kirstenson playtested an English-language version back in the '90s, which suggests a North American release almost took place.
It would appear that the unreleased version has just been acquired by a private collector. An eBay seller claimed to have had a copy of Taloon's Great Adventure (the proposed Western title) for sale at €50,000 (or around $53,000).
The prototype apparently came "from a former Nintendo employee who had access to Product Analysis... the prototype was in private possession for a good 20 years and was never publicly exhibited or given away."
As you can see from the tweet above, attempts were made to try and strike a deal and preserve this piece of Dragon Quest history, but it would seem that the seller got a better offer – which means the game will almost certainly remain "lost" until its new owner decides to cash in.