The Cat Carrier (White Kitten) is sold by Lil Timmy in Stormwind for 60s, with only one kitten for sale each time Timmy appears. This makes it a very rare pet, and an impossible one for Horde players to acquire by direct means.
Buyable white kittens are all female, as evidenced by Lil Timmy's quote "I can't believe dad won't let me keep your sister", said to his other kitten.
Due to the rarity of this pet, it fetches a high price at the Auction Houses around Azeroth. Horde characters are often willing to pay a fair bit of gold for this pet since it is only obtainable by Alliance characters (unless Neutral Auction Houses are used). Auction prices of White Kittens can reach 100g on Alliance Auction Houses and even higher on the Neutral Auction Houses.