Shnoop via eBay offers the Oral-B Power Sensitive Extra Soft Replacement Electric Toothbrush Head 3-Pack, model no. EB17-3 ES, for $13.99 with free shipping. That's the lowest total price we could find for this quantity by a buck; most stores charge over $20. It's compatible with all Oral-B rechargeable handles, except for Oral-B Sonic toothbrushes.