NeweggFlash offers the Aukey Quick Charge 2.0 18-watt USB Car Charger with 3.3-Foot Micro USB Cable, model no. CC-T5, for $3.99 with free shipping. (Aukey Direct via Amazon charges about the same via coupon code "JPEQHDZY" with free shipping for Prime members.) That's the lowest total price we could find by $8.

Update: It's now sold out at NeweggFlash; however, Aukey Direct via Amazon charges $4 via coupon code "JPEQHDZY" with free shipping for Prime members.