I want to thank you for asking about this "designer" cat stuff. That's all it is - a money making thing from either poorly informed people or GREEDY people looking for an unsuspecting person so sell their overpriced, bad quality kittens.
Its all a gimick. What your friend should do, is to attend a cat show locally and talk to breeders that she likes about getting a quality kitten. Doesn't have to be show quality - breeders do have pet quality cats - which are just as healthy, but may have a minor flaw in them that they can't compete. Like in a persian you might have ears too big or nose too long. But you still get a good cat who's had just as much care as her show quality brother
Some things to consider - do NOT get a kitten from a breeder who is selling them to new homes under the age of 10 weeks old - they need time with mom/siblings up till then to become a better cat mentally and physically. Plus your kitten would have all their shots and probably be neutered or spayed (covered in the cost of the kitten).
Expect to pay several hundred dollars. Sometimes "cheap" is not better - you wind up with more health problems which cost far more then the initial price you'd pay for a good breeder's kittens.
Also I hope you will discourage your friend from getting a kitten from a pet shop!
They come from backyard breeders and kitten mills - both are NOT good places to get a kitten (besides they are way overpriced).