For its Prime members only, Amazon offers the Caldwell Low Profile E-Max Electronic Ear Muffs
in Green, model no. 487557, for $16.99
with free shipping
. That's the lowest total price we could find by $16. Designed for shotgun and action shooters, they feature a microphone to amplify sounds under 85dB, which shuts down for sounds above that level. It requires two AAA batteries (not included).
Of note, these will ship in three to four weeks.