The Iconic via Amazon offers the Iconic 5,000mAh Battery Case for Galaxy S8 for $39.99. Coupon code "DEALNEW2" cuts that to $29.99. With free shipping, that's the lowest price we could find by $10.
They also offers the Iconic 5,500mAh Battery Case for Galaxy S8 Plus for $29.99 with free shipping, via the above coupon. That's $70 off and the best price we could find. Both deals end June 30.