How much is a blue British shorthair cat?

Pet quality - at LEAST $600. More likely around $800 as the breed is not as common as other breeds. If there isn't a TICA, CFA or ACFA breeder near you then add in several hundred to fly to the breeder and if approved to buy, the cost of flying home with the cat in the cabin - another $100 or so.

Show quality - into the thousands.

Most all purebred cats will cost you about $600+ for pet quality kittens.

Didn't pay $00.02 for my Thomas (Dumbass).

I drove my school bus to a neighbouring village a few Winters ago and Thomas hitched a ride home in the engine compartment and hid there for three day. It was a year before I found his breeder owner and she let me keep him because I'd had him neutered.

Of, course, she diplomatically deflected my request for his papers - LOL .

They range... I'd say from £350 to £500!

[edit] I'd also say it depends on where in the UK you live, down south they would be more in the £450+ range

i live in the west midlands (uk) and they are only 50 pounds to 100 here