Clas Store via Amazon offers the X-Preen Air-Cushion Transparent TPU Case for iPhone 6 for $9.99. Coupon code "6ZS4XVFJ" drops it to $2.99. That's $17 off list and the lowest total price we could find. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.05.)
It's also available for iPhone 6 Plus for $3.99 via coupon code "7U3II5TO". With free shipping for Prime members, that's $16 off list and the lowest total price we could find.