Hello A few answers.....
So, That was/is a COMMERCIAL Filter Queen by HealthMor that was manufactured roughly from the 1960's thru the 1980's, as I have seen them in the darker chocolate brown before which would indicate a time of that late. I could be wrong, but...unless someone can correct me with better information; lets just go with that timeframe....
They were designed for large homes and commercial type properties. The extra large dirt tub, the wide floor brush and such are very clear indicators of that aim. This was manufactured for a time just like the Electrolux CB model, which it competed with along with others for the relatively small, or not as great as an upright's commercial canister/tank business.
Again, I have no idea how long they were ACTUALLY sold, maybe someone else can verify this, but I've only ever seen a handful (5-6) in the last 25 years so. And, as to it's value?
It's going to be whatever you can find as an offer for it. Granted that it being absolutely NOS (New old stock), and in museum quality shape will be a benefit, as a actual vacuum it will be limited to those who have ready access to 220v power, and over here in the U.S. where the market for such an item would be rather high; unless they had a converter or a dedicated power , it willbe useless as it cannot be run (to my knowledge) well or properly on 110v.
There are people who like FilterQueens fine, so it may not be an issue whatsoever. You could do a silent auction/ seal bid kinda thing, or list it on eBay and see what you end up with. That is the most accepted/best way to not only play fair to all, but use as a "what is this vacuum worth". If you must know cold hard numbers I would wager to say anywhere from .....roughly $150 to 300- . You may find someone that must have it an they will bid the world.
My advice to would be sellers is always when asked for it is: Don't plan a vacation, a retirement, or even a trip to buy anything extravagant off the proceeds of what is essentially an old vacuum cleaner. Remember it's just a vacuum. It had a certain price when new, most of us know that price, and unless it's an absolutely MUST have; it will have only one final price NOW when sold. Yes again, it's a nice one to be sure, it may make you a small fortune, but that's VERY rare. Keep in mind too that there are always more to be had (maybe NOT in that condition), and most collectors do have a limit that they will spend for anything. Some don't yes, but once again they are a pretty small lot.
Good luck to you. It looks beautiful, and if I was a FQ junkie I would be all over it.
Chad