Costco's latest coupon book valid 9/1/16 through 9/25/16 has $20 off the Waterpik Ultra & Nano Water Flosser Combo
. YMMV. My local Costco (in Northern California) has it priced for:
$79.99 - $20 = $59.99 which is lower than it is on Amazon by $10 ($70 on Amazon). This version comes with an additional Nano Watperpik that's good for travel and/or business trips. Also, comes with more brush heads than the individual versions.
Though I have not tried it myself, I believe you can purchase this online via Google Express as well,