Walmart has the 2-Pack Ozark Trail 5.5" x 20" Inflatable Boat Bumper Fenders (Blue or Black) for $15 with free shipping with Walmart+ (free 30-day trial), $6 shipping, or free shipping on $35+.

Also available in 6.5" x 2.3" for $20, while the 8.5" x 27" size goes for $25.