TomTop offers this Classic Mobile Games iPhone Case in White or Black for $13.99. Coupon code "DSCMGPC " drops that to $9.99. With free shipping, that's the lowest price we could find by $3. It includes various playable games (including a Tetris-like game) and is available for iPhone 6, 6s, 7, and 8 as well as each Plus model. (The compatible phone type is listed under the product name when you select/change the color option.)

Note: This item ships from China and may take up to four weeks to arrive. The countdown timer on the product page does not reflect an actual expiration time and resets daily.

Update: The price has dropped to $8.99. The coupon no longer applies.