Hi Kimberly,
There are some Laundromats around but they actually aren’t that common. The ones there are run on Costa Rican coins.
But what most travelers do when they travel is use a laundry service. You might drop it off at the front desk of your B&B or hotel, for example. It’s usually not that expensive as long as you’re not in a fancy hotel or resort. Or in many towns you’ll also see signs up advertising laundry service done by local people in their home. You drop it off and pick up later that day or the next day. Again, very reasonably priced.