Newtrent offers its Newtrent Tempered Glass Screen Protectors for iPhone 5, 6, or 6 Plus for $11.95 each. Coupon code "SUMMERBLAST" cuts it to free. With $3.54 $1.95 for shipping, that's $14 off and the lowest total price we could find. It resists scratches, fingerprints, dust, and normal wear.

Update: Shipping updated; select "First-Class Mail Parcel," and then shipping will drop to $1.95 at the final stage of checkout.