Walmart offers the Waterpik Cordless Water Flosser, model no. WP-360, for $29.99. Opt for in-store pickup to avoid the $5.99 shipping charge. (Best Buy charges the same price via pickup.) That's the lowest price we could find by $7, although we saw it for $2 less last September. This rechargeable flosser includes high-pressure and low-pressure tips, and is purportedly twice as effective as string floss.