I used these after a flood in my apt, no power and reusable. It was under $10 and sold at places like Walmart.

Protect against dampness, mildew, rust, and musty odors in closets and other enclosed areas with the unscented calcium chloride pellets of Dry Out®. Moisture is drawn from the air without the use of an expensive electrical appliance. Use one jar for the average reach-in closet, two or more for larger walk-in closets. Check the jar every two to four weeks and pour off accumulated water as necessary.