Responsible breeding can involve health screening, veterinary care, appropriate nutrition, registration, suitable housing and substantial time caring for kittens. Those costs help explain why a carefully bred pedigree kitten may cost more than an informal advertisement suggests. However, a high price does not prove that any of those standards have been met. Ask what screening was performed, what the results mean and which documents you will receive. A seller should be able to explain their process without relying on words such as exclusive, giant or rare.
Compare the care and transparency behind the price rather than assuming the most expensive kitten is the best choice. Also consider adoption if a suitable cat is available. Whatever route you choose, protect enough of your budget for ongoing care; spending heavily at purchase should not leave essential veterinary or daily needs unaffordable. Ask for actual dated results rather than a logo or the phrase health tested; the useful detail is which parent was screened, how and when.
For product comparisons alongside this advice, see Velvet Nest and Sterling Court litter tray. The details below explain their sizes and uses.
Further reading: cats.org.uk; cats.org.uk; gov.uk; gov.uk; gov.uk.
Velvet Nest
Sterling Court litter tray
Taj-MeowHall