These rifles had their heyday in the 1980s as a cheap, powerful alternative to the mighty Weihrauchs that ruled the roost. They really were not as good as their German competitors - the trigger was far inferior, as was the breech lock up.
A really good standard Vulcan today might fetch £90-100 from a collector. There was a rarer walnut stocked version that is probably worth 50% more. Buy to fill a gap in the collection or as a fun gun but not for serious shooting.
IMHO its competitor the Mercury from BSA was a much better rifle.
Adrian