In today market, probably $800+, which is absolutely rediculous for such a piece of crap gun, but then, thats about what the open bolt Cobrays were going for the last time I saw one, and they aren't a good gun either.
open bolt guns are really, really frowned on by the BATF, and even though technically still legal, nobody will make them anymore. IT has to do with the "readily convertable to full auto" language in the laws.
Back in the early 80s the ATF was in court with Cobray over their guns, and while I'm not sure exactly how it was finally settled, I do know that some dealers were "discouraged" from delivering the open bolt guns to customers at that time. And, Cobray did change their M11/9 to a closed bolt operation.
As a collector's item, the Demro is an example of an era. As a good shootable gun (that will last) its not. They were cheap junk when the Tommygun (semi) sold for $250. They're still cheap junk, just able to bring more cash on the market today than when new.