Sad Cat
The Sad Cat is an EXCLUSIVE pet that was on sale in the Exclusive Shop for 1,299 Robux. It was introduced in the Steampunk Update. It is no longer available unless through trading.
The latest Pet Simulator X value list for Sad Cat can be found below:

Regular
💎 36,000,000,000 (36b)

Golden
💎 Not Available

Rainbow
💎 Not Available

Dark Matter
💎 Not Available