The text mentions the cheetah and jaguar but doesn't specify to use those stats from the beastiary. I'm planning on using one in an upcoming game where the GM can be a bit rules lawyer-ish. So do we intact use those stats?
Character concept has a snow lynx (who will eventually become an AC (cat, small)
Cheetah: Bestiary page 40
Jaguar: Bestiary page 40 (Leopard)
Note: If you buy a cat it would be a bit strange that it shrinks in size from Medium to Small when you first acquire an animal companion. Also, while the "Cat, Small" listing states "Cheetah, Leopard" the stats are that of a Cheetah and not a Leopard (it has Trip and Sprint instead of Pounce and Rake).
Cat Stats Fever!
You'll probably want the Small Cat stats for animal companions listed under the Druid class: http://paizo.com/pathfinderRPG/prd/classes/druid.html#_druid
Considering tiny cats are 3 cp and Medium sized fightin' cats are 100 gp, I'd probably try to argue a smaller cat might be a bit cheaper. A guard dog is 25 gp for example, while a riding dog is 150 gp. Worth a shot.
EDIT: I'm assuming you're looking to have the animal on hand before it actually becomes your companion, right?