The 420 Military Stock rifles are in short supply, so while you CAN buy one for about half that (they come up every four years or so...), it would be from a person who didn't know its value and was just selling it off as 'an old airgun'. Probably less than 100 were sold in the UK, and there was more than one stock style. Collectors don't seem to have got THAT interested in Hammerlis, although they were one of the best mid-priced rifles available in the 1970s, astonishingly accurate with superb triggers.
I would buy one for £195 if it was in excellent condition, no problem. In fact I want to buy the one you are talking about!
Apart from that, they are extremely accurate and sweet-shooting rifles, if you are actually going to use it. I would get it and treat it well. Beware the enormous spring they have, the longest of any springer I know of (15").