At Best Buy, buy one The Sims 3 game or expansion pack and get a second for free. (Add two to your cart to get the discount during checkout.) With free shipping, that ties our mention from three weeks ago (which was via Amazon) and puts many pairs are at lowest-we-could-find prices. Sales tax is added where applicable.
A best bet is to nab The Sims 3 for PC or Mac together with The Sims 3: Pets Diigital Download for Windows for $39.99 with free shipping. That’s the lowest total price we could find for the pair by $3.