Go to Settings -> Extras Click Add New Enter values for Name and Price. Click Save.
This is similar to deleting a service, except you can always restore an archived item. Go to Settings -> Services Click the Archive button next to the Service you want to delete When the [...]
You simply have to add the Price of the Service at the end of its Name. Instead of: "One Bedroom Apartment Cleaning" type the Name as: "One Bedroom Apartment Cleaning – $99 "