$6K for a STEN Mk II built up as a long-nosed, striker-fired semi-auto? At the end of the day, despite being relatively rare, it is still an $8 (in 1944) stamped and spot-welded "Plumber's Nightmare" of a pseudo-submachinegun. You could buy 2 B+T APC9 PCCs for that money. Or a NR, Open-Bolt, factory semi-auto Franchi LF-51 that is currently on the EE with the factory short barrel and 3 mags for the lesser sum of $5400, which is still about $3K too much for that particular "Unicorn". Personally, I wouldn't pay more than $2K for a tarted-up STEN Mk II that anyone can own in Canada. Of that money, $1992 would be for the NR status and $8 for the gun itself.... (JK!)
Obviously, YMMV, but that is how I would honestly value that firearm. They really did earn their reputation as the cheapest possible solution to the problem of mass-producing a new submachinegun in the aftermath of the British Army's evacuation from Dunkirk. Unless you REALLY, really need a STEN for your collection, I would buy just about any other, more modern NR PCC. They will be far better quality in terms of their basic design and metallurgy and, will likely be a heck of a lot more fun to handle and fire.