Amazon has the 3-Pack Castrol GTX Full Synthetic 5W-20 Motor Oil (5qt jugs) for $71 - 40% off coupon (check "Save an extra" box, eligible on first S&S order for this product) = $42 with free shipping. (Extra 5% off for 5+ subscribe and save orders)

Roughly $14 per jug. The 40% coupon is also showing up for some users on the 5W-30 and 0W-20.