Best Buy offers StarCraft II: Wings of Liberty for Windows and Mac for $19.99 with free shipping. Outside of the prices below, that's the lowest total price we could find by $14, although we saw it for $2 less six days ago (since expired). (For further comparison, most merchants charge over $40.)

Of note, Amazon charges the same for its Prime members but has a two to three week backorder; newegg also charges the same for its newsletter subscribers via coupon code "EMCXTWV22".