UltraProof via Amazon offers the Tethys Waterproof Case for Smartphones in Black, model no. UU-WC-01BLK, for $8.49. Coupon code "Z53IU4SS" cuts the price to $3.99. Plus, Prime members qualify for free shipping. (Non-members can spend $35 to qualify for free shipping; otherwise, it adds $6.01.) That's $16 off list and the lowest total price we could find. It's compatible with several smartphone models, including the iPhone 6, iPhone 5S/5C, Galaxy S6, LG G2, and HTC One M8.