K&N Motor Oil: 5W-20 Full Synthetic Engine Oil: Premium Protection, High Mileage, 4 Quarts – $15

$14.99 for 4 quarts (NOT 5 quarts) with coupon
($13.74 each with 5 item S&S)
you can only order 1 at a time for the coupon to apply but you can order multiple times.
I just ordered 7 4-quart bottles individually with S&S for 13.74 each. AND NO REBATES! (price is equivalent to $17.18 for 5 quart bottles)
there may be coupons for other k&n full synthetic oils but havent checked. Goodluck
https://www.amazon.com/dp/B08MVG9VF2