Amazon.com also has Genkent Replacement Brush Heads For Oral B Toothbrush Precision Clean 20 Brushes on sale for $10.59. Shipping is free. Thanks.!!
Note: Usually ships within 2 days.
https://www.amazon.com/Genkent-Replacement-Toothbrush-Precision-Brushes/dp/B00RCK2JAU