ebestshop4u via eBay offers this 16-LED Solar Motion Sensor Security Lamp for $8.99 with free shipping. That's the lowest price we could find by $7, outside of other eBay vendors and the mention below. It features a 50,000-hour lifespan and is waterproof.

A close price: Yescom via Walmart has it for $9.39 with free shipping.