Select "One-time purchase" to save extra $4 at checkout. Amazon has the 50-pack RefreshPlus Lubricant Eye Drops (0.01 fl. oz. / 0.4mL Single Use Containers) for $15.99 - 20% off coupon (check green "Save coupon" box) - $4 off automatically at checkout ("Extra Savings") = $8.79 with free shipping on $25+ or with Prime.

Note (YMMV): you *may* be able to combine with Subscribe & Save and save an extra 80 cents at checkout.