TomTop offers the Retroflag NESPi Case Designed for Raspberry Pi 3 / 2 / B+ for $22.99. Coupon code "NESPI" cuts it to $17.39. With free shipping, that's the lowest price we could find by $3. It features functional power and reset buttons, LED power indicator, SD card slot, and two USB ports.

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

Update: The price has dropped to $16.99. The coupon no longer applies.