Yugster offers four Replacement Brush Heads compatible with the Philips Sonicare E-Series Toothbrush for $14.97 with free shipping. (Amazon has a similar set for about the same with free shipping for Prime members.) That's the lowest total price we could find by $15. The brush heads are compatible with Sonicare E-Series, Sonicare Advance, CleanCare, Elite, Essence, and Xtreme Power toothbrushes.
Note: The countdown timer on the product page does not reflect an actual expiration time and resets daily.