Sonifresh via Amazon offers its Sonifresh Replacement Toothbrush Heads 4-Pack for $11.39. (Select the "one-time purchase" option.) Coupon code "4LSYRYLY" cuts it to $6.23. Plus, Prime members receive free shipping. That's $6 off and the lowest price we could find, although we saw it for a buck less two weeks ago. They're compatible with a range of toothbrushes including Philips Sonicare FlexCare, EasyClean, HealthyWhite, and Diamond Clean. Deal ends December 28.

Note: Non-Prime members can order via Subscribe & Save for free shipping. Be sure to cancel your subscription after your order ships to avoid being billed for subsequent purchases.