The Sims 3 is on sale at Direct2Drive (D2D) today as their Mac Monday Deal for $19.98. Same price for the PC version. Use a 15% off promotion code such as F7530AEE8D991B19332624D10F9C734F to make it $16.98. (If the coupon has expired you can get a new one by clicking here.)
The Sims 3 Deluxe version is also on sale at Amazon for a Mother’s day promotion as PC Digital Game Downloads for $29.99. The Deluxe version comes with The Sims 3 and The Ambitions Expansion DLC. I think the other DLCs are also on sale at Amazon currently.