Ferrets are now available in Happy Pets for players Level 40 and above. As usual, level-access does vary, as does price. The ones available for coins, costing 20,000 Coins and up, are: Cream, Snowy, Sable, S'more, and Lemon. The premium ones requiring 64 Facebook Credits are: Pink, Firehouse, and Blueberry.
But the Caramel Ferret is free, cause you can only get it through other players' orphaned animal Wall posts on your Live Feed. (Note: Unfortunately, along with this announcement comes the news that the White Rabbit, Baby Blue Bunny, and Lavender Bunny are no longer available via Live Feed.)