Amazon offers Prime members Stargate on Blu-ray / Digital HD for $4.96 $5.04 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $4.98.) That's the lowest total price we could find by $6. It includes both the theatrical and extended editions.

Update: Note that this item is temporarily out of stock, but can still be ordered at this price for delivery when available.