Meritline offers the Oral-B Precision Clean Brush Head for 4-Pack
with free shipping
. At $1/brush, it's the lowest total price we've seen for Oral-B toothbrush head refills of any kind, in any quantity. (It's currently a buck under the best we could find even for one
Precision Clean replacement head elsewhere.) They're compatible with several Oral-B electric toothbrushes.