Holmes Window Fan with with Twin 6-Inch Reversible Airflow Blades – Link

Amazon has this currently marked down to only $15.05!

• Dual-blade operation for a powerful, cooling breeze
• Two speed settings and manual-reverse airflow control
• Water-resistant motors are safe to use during rainy weather
• Designed to fit most double-hung and slider windows
• Adjustable extender screen and extender panel help secure fan in larger windows
• Ideal for large rooms up to 500 sq. ft.