Groupon offers the Oral-B Compatible Replacement Toothbrush Head 12-Pack for $9.99 plus $3.99 for shipping. (A 16-pack is available for a buck more.) That's $4 under our mention from August and the lowest total price we've seen. (It's a current best by $4, excluding the mentions below.) They're compatible with a wide range of Oral-B toothbrushes (listed on the product page) and feature soft bristles and color rings.

A few close prices: Bahhinc via eBay offers a similar set for $14.99 with free shipping. Mary's Market via Amazon also has a similar set for $14.99 with free shipping for Prime members.