You really do have to be aware of the costs of a kitten, they aren't cheap animals by any means. In fact purchasing the kitten will probably be the lowest cost you'll pay.
We have a pedigree cat and, until recently, a moggie. I shall tell you the costs of moggie ownership.
Our moggie cost £50 to buy from a local family, there were no suitable cats in the shelters and no free ones. She needed a course of vaccinations, this cost £75. Then microchipping, £20. You can get worming and flea medicine cheaper if you order off the internet, but I would budget about £4-5 a month for them. If your cat is going to go outside then they will need worming and fleeing, and the vaccinations, as they will be mixing with other cats.
Toys can be cheap, cats love ping pong balls and crinkled up paper and tinfoil. You'll need food and water bowls, a litter tray and litter (litter costs vary from £2 a bag for fullers earth clay to £8+ a bag for the posher, dust free stuff). They will need a scratching post so that they don't use your furniture instead, they can be from £5 to £150 depending on size and quality. You can buy a bed but my cats have always ignored them, preferring our furniture instead!
Food can vary in price, and I won't lead you into a discussion about whether cats need all the grain in them or not. Lots of cats do live happily on the cheaper food. Unfortunately one of our cats has a grain intolerance so needs special food which costs up to £30 a month. They often need special, easily digestible food when poorly too.
When they are 5-6 months old they will need neutering. This costs between £80 and £120 usually. Neutering is very important, you don't want to bring unwanted kittens into the world.
I recommend pet insurance wholeheartedly. We use pet plan and the For Life plan was £8.50 a month for our moggie. It does not pay for worming, de-fleaing or neutering, you need to find the money for them yourself. Our plan has an excess of £65, which means that you have to pay the first £65 of any illness and the insurance will pay the rest, though they look through your bill with a fine tooth comb and inform you of anything they won't pay for. You will often have to pay for the treatment at the vet before claiming, and then they refund you when the insurance company pays them.
Each time you visit the vet it will cost you £25-£35 in consultant fees, plus any medicine (can be £10 for an injection, £20 for a course of tablets etc).
There are emergencies which you need to factor in, and this is where insurance helps BIG TIME. Our moggie kitten developed a very rare, terminal illness called FIP. She was only 8 months old. For two weeks we battled to cure her, but there was no hope and she was put to sleep before she got worse.
The two weeks of treatment included vet visits, medicines, 6 days in the vets on a drip, emergency appointments on the bank holiday, special food, many blood tests, a trip to the big veterinary university and a biopsy. The cost came to over £1200, thanks to pet insurance we had to pay only £95 of that. Pet insurance gave us the opportunity to do everything we could to try and make her better without worrying about the costs. Pet Plan were very good to deal with and I recommend them.
Another thing you need to think about when taking on a pet is the amount of time they need. Unless a friend, family or neighbour can come in to feed and scoop their poop twice a day when you are on holiday, then you will need to put them in a boarding cattery. This can be very expensive.
Please do some thorough research before getting a kitten of your own, the library will have some books that you can borrow!