iSelector via Amazon offers the iSelector Waterproof iPhone Case for iPhone 6 in Black or Yellow for $19.99. Coupon code "YCWWI79V" drops it to $10. Plus, Prime members bag free shipping. (Non-members can spend $35 to bag free shipping; otherwise, it adds $6.33.) That's $32 off list and the lowest total price we could find. It's water resistant, shock/dirtproof, and includes an armband.

Also available is iSelector Waterproof iPhone Case for iPhone 5 / 5s in Black for $10 via the above coupon. (Prime members again bag free shipping.)