iNetVideo offers Assassin's Creed: Director's Cut Edition for Windows, for $6.99. Add it to your cart and it falls to $4.04. With $2.95 for shipping, that's the lowest total price we could find (outside of the price below) by $13, although we saw it for $2 less in March (which also included a credit good for a free second game).
A close price: Amazon sells it for $7.48 with free shipping via Amazon Prime.
Assassin's Creed Director's Cut (pc Dvd Game), a similar product, is available at these stores