We acquired six kittens when our cat gave birth last year:
We kept two of them (and the mother) but for the seven or so weeks between birth and giving four of them away we had a blissful house of kittens
It is very easy - soon after you get them register with a vet near to you (or convenient for dropping off on your way to/from work) and get them inoculated and dewormed at 9 and 12 weeks and then they are set up for life and can go outside without risk of catching diseases - the inoculations cost around £55 per cat. The vet can also give them a general check to make sure they are developing normally.
Then get them neutered at six months (unless you want some more kitties) - a cost of around £80+ for females, £60 for males.
Add in also cost of getting started - basket, bowls, litter tray, cat litter etc and maybe cat flap. I think realistically you will need a litter tray as tehy will use it until they can go outside and at night time if you dont have a cat flap
Then add cost of ongoing flea treatments and worm treatments (eveyr month / 3 months) and cost of kitten food (which seems to be around £1 more than normal cat food) and treats. According to the manufacturers they can move onto normal cat food at 12 months but otyher owners I know have moved kittens on to adult food at around 6 months with apparently no ill effects.
Register with cat food manufacturers for free samples - people like
http://www.catslikefelix.co.uk/sample/,
http://www.purinaone.co.uk/uk/cat/sampling/,
http://registration.mars.com/oods/WhiskasCarePack.aspx but be prepared to accept the fact that the kitten/ cat wont like anything but the most expensive brands of cat food and will have a tendency to change preferences to another brand just as you buy a bumper pack of a particular cat food!
We havent had any need for further vet treatment and dont have insurance but obviously will face big bills if something major were to happen - I'm banking on the fact that it wont!