Walmart offers the Eva-Dry Renewable Mini Dehumidifer for $14.97. Choose in-store pickup to avoid the $5.99 shipping fee. (Home Depot charges the same, and Amazon charges the same with free shipping for Prime members.) That's the lowest price we could find by $5. This dehumidifier uses a renewable silica gel technology that works without batteries or power.

Update: It's now out of stock at Walmart; however, Home Depot and Amazon still offer it for the same price.