Normally, I wash my own clothes and hang dry them at my apartment but sometimes items are too large for my tiny washer so I have to head to a laundry service. The cheapest Lavanderia in my neighborhood is Lavanderia Autoservicio Buenavista. It is in Lavapies and although it isn’t the most convenient location it is one of the cheapest I’ve found. One wash costs 4 € and a dry for 30 minutes costs 4 €. In the past at other places I have paid up to 7 € for a 30 min dry and the clothes still came out wet. So it doesn’t hurt to shop around for better prices, especially when you need to wash and dry a queen down comforter in the wintertime. It takes forever to dry things inside during the winter here. This lavanderia also has free wifi so you can surf while you wait. Or just drop your stuff off and the guy that works there will take care of everything.
They are open everyday except Sunday and of course only take cash. He provided the detergent free of charge and was just a super friendly dude.
Check them out if you need a wash in the neighborhood:
Lavanderia Autoservicio en Madrid Centro