Amazon has The Sims 3 Pets for both consoles at $29.95. Cheapest i have seen it.
360
http://www.amazon.com/Sims-3-Pets-Xbox-360/dp/B0054IUY22/ref=sr_1_5?ie=UTF8&qid=1320637896&sr=8-5
PS3
http://www.amazon.com/Sims-3-Pets-Playstation/dp/B0054IUWSI/ref=sr_1_9?ie=UTF8&qid=1320638083&sr=8-9
360
http://www.amazon.com/Sims-3-Pets-Xbox-360/dp/B0054IUY22/ref=sr_1_5?ie=UTF8&qid=1320637896&sr=8-5
PS3
http://www.amazon.com/Sims-3-Pets-Playstation/dp/B0054IUWSI/ref=sr_1_9?ie=UTF8&qid=1320638083&sr=8-9