Amazon has the 4-Pack of Soylent Plant Protein Meal Replacement Shakes (Vanilla, 11oz each) for $10.98 - 5% off with Subscribe & Save (can cancel anytime) - $4.99 off coupon (check “Save an extra” box, eligible on first S&S order for this product) = $5.44 with free shipping on $25+ or with Prime. You can use the coupon three times, so it's $16 for three 4-packs (12-ct total).

Target has 4-packs of Strawberry and Vanilla for $5.99 after 50% off Target Circle coupon [Exp 7/18].