Amazon has the 20-Pack of STK Extra Thick Magic Cleaning Sponges for $6.10 - 5% off with Subscribe & Save (can cancel anytime) = $5.80 with free shipping on $25+ or with Prime.

Order two 20-packs (40-ct total) for $11.60 and get a $10 Amazon credit to spend on Prime Day (6/21 & 6/22) with purchase (Small Business Promo).