Home Depot offers the 3M Tekk Protection Shotgunner Earmuff in Red, model no. 97013-00000, for $10. Choose in-store pickup to dodge the $5.99 shipping charge. (Amazon charges the same with free shipping for its Prime members.) That's the lowest price we could find by $15. These ear protectors feature a 21dB noise reduction rating.

Update: It's now sold out at Home Depot, but Amazon continues to offer it for the same price.