iOttie via Amazon offers Prime members the iOttie RapidVolt Dual USB Car Charger in White or Black for $7.50 with free shipping. (Non-members can spend $35 or more for free shipping; otherwise, it adds $5.01.) That's the lowest total price we could find by $4. It features a green LED power indicator, 2.5-amp output per port, and Smart Charging (to stop charging when battery is full).

Update: Both models are now available for free shipping without the need for a Prime account.