Getting a pure breed cat will be expensive and, if you've never had cats before, very unwise. Pure breeds often come with personality problems because of the way they are bred, and it takes an experienced pet owner to know how to handle them.
Buying from a pet store is also a bad idea - you don't know their history, and it's common for them to be weaned too early so the shop owner can sell them earlier. You wouldn't know whether they were healthy and what the circumstances of their sale are.
By far the best thing to do is adopt a kitten from a local cattery / RSPCA branch. The kittens there are all vet-checked, screened for health problems, micro-chipped and not weaned until they are ready. Adopting usually costs around £40, but that often includes free neutering when they reach 6 months of age; so in fact you're saving a lot of money. Plus, the money goes to help other cats.