Actually, you ought to be able to pick up a second-hand S400 for about £250 without a scope but then I guess you meant with a scope.
As you've been repeatedly
you'll struggle to get a rifle and scope worth having for £250.
get an S200 with a scope for £250 if you were lucky. The S200 is a great gun and ideal for HFT and a bit of hunting too.
The best place to be looking (and it pains me to say this!
) is the Airgun BBS. Browse the ads for a bit and you'll see plenty up for sale but whether you'll find what you want for the price you're looking for I'd doubt.
If you had another £25 I reckon you'd stand a much greater chance.