The Webley MKIII is a really beautiful rifle.
It has some really lovely open sights, and best shot that way.
The bell target ones even nicer.
They shoot perfectly well at bell target and within the farm yard; they are just not a HW77.
There are plenty about, but few in superb condition.

So whats not to like? Condition is everything and the better ones will demand hansom prices. Others just healthy prices.
I don't think prices have changed that much and just depends on the market that minute, or the sales room enthusiasm. A nice one should be under £200, and a superb one £300, all +/- £30. They aren't £650 rifles. People just love them, and for very good reason. I sold my father's 40 years ago to get a FWB Sport, and for good reason too.