Amazon has Oral-B Precision Clean Replacement Brush Head (4 ct.) for $12.48 plus shipping. Use subscribe & Save and the price drops to $10.61 with free shipping.
Product Features:
* Advanced bristles system: Removes more plaque than a regular manual toothbrush
* Interdental tips: Penetrate hard-to-reach areas
* Indicator® bristles: Fade halfway to signal when to replace your brush head
* Cleans deeper than a regular manual toothbrush
* Penetrates hard-to-reach areas
Amazon.com: Oral-B Precision Clean Replacement Brush Head (4 ct.): Health & Personal Care
Oral-B Precision Clean Replacement Brush Head (4 ct.) $10.61 + FS 
