Hi Mark.
You're right that blowback pistols don't tend to get many shots per capsule. Typically around 40. There are also "half blowback" types which get around double or even well over 100. These tend to be mostly bb guns which have smoothbore barrels and are not as accurate as a rifled barrel which shoots pellets.
You seem like you're leaning towards a revolver and you'll get the most efficient use of gas plus multi shot capabilities.
There are lots of fine revolvers around and your choice will largely depend on your taste.
Modern styles like the Dan Wesson 715 are well made and accurate and can just about be picked up inside your budget.
For older styles like the Colt SAA and Schofield you'll need to go up to £170-£200. You could always consider used of course.
A personal recommendation would be the Crosman 357 or its updated version the Vigilante. You'll get a proper rifled barrel and fully adjustable sights. The only downside (for some) is a plastic barrel shroud and only the front part of the cylinder rotates. They're very accurate though and a joy to shoot. You'll get around 80 shots per capsule and will shoot pellets and bb's.
For single shot I'd highly recommend the CP1 pistol. These can be bought from Poland for less than £70 and are very accurate. There's a version with a rotary magazine but I wouldn't bother with that as it doesn't work well. Only about 40 shots per capsule but they're a powerful pistol.
Hope you find something which suits.