Hi
I'd look around for a Baikal IZH-53, you should be able to get one new for about £60 if you shop around, or a secondhand one for less if you're lucky. Although they're cheap they have a good trigger and barrel, and can be upgraded easily and cheaply by fitting a better spring guide if you're minded.
Other than that I'd suggest looking at secodhand pistols. When you say "casual target shooting" do you mean plinking? You could do much worse than buy a Webley Nemesis, Tempest, Hurricane, or even a BSA Scorpion from the "Sales" section on here if so. Some Gamo pistols are ok, you could probably get a Hatsan pistol in your budget but for target shooting the heavy triggers on the cheaper pistols will hinder accuracy.
I'd steer clear of Co2 guns for a first airgun, they can be unreliable and a bit finicky, though lots on here seem to like them. I'd look for a springer first, no cartridges to buy, just pellets!
Welcome to the forum by the way!