If you're looking to make a little extra cash, you might consider selling your mattress. In this case, you will definitely want to have your mattress professionally cleaned, which will cost you approximately $55 to $80 depending on the type of cleaning service you choose [source: Johannes]. Once you've done so, post your mattress on craigslist.com or another similar site. Be sure to include a photo showing your mattress is clean and free of stains, and add a detailed description of how it's been cleaned and maintained to attract the most buyers. You should also note the brand, a description of its firmness and other features, as well as the price you paid for it. Although you won't get anywhere close to the cost you put into the mattress, this helps build the legitimacy of your post. A second-hand shop in your community might also purchase your gently used mattress. Search for shops online and call ahead to make sure they purchase mattresses.