On eBay, a plastic exterior dryer louvered vent cover costs between $5.38 and $8, as of February 2015. The price of an exterior house vent cover depends on the type of vent and the materials that are used.
Low-cost vent covers tend to be of either gray or white plastic louvered design. This design lets air pass through the hinged slates without letting in outside air. Exterior vent covers also stop dirt and debris from entering into the vent and the ducts for dryers or heating and cooling units. In addition, vents over crawl spaces prevent animals and even people from gaining entry into a building.