I used to dry FB prints with a hairdryer. It's a labour intensive method but gets prints flat enough to finish off under a pile of books. Squeegy away excess water and point hair dryer at one side of print from about one foot away. As soon as it curls towards the hair dryer, point at reverse side. Continue the process. Towards the end the print will hardly curl at all when heat is applied. Typically, the print will be flat or show a very slight upward or downward curve that can be cured by weight.

Cheap, but time consuming.