Mmmm yeah just checked and the cheapest I found on ebay was 138€ from Poland. Much pricier that I remembered (but I just can't find THAT offer) but still a long way from the 350 you are suggesting.

There also was another device I've looked up some years ago (when it was of no urgency as my best monitor at that time was a Dell featuring DualLink) that would go for about 100$/€ but I just can't remember what that actually was.