Amateur pilot in the North Eastern US.  Going to Portugal in June and I would like to take my drone with me.  I have a UAS pilot lic here in the US.  
Looks like I need a EASA  UAS certficate.  I am only seeing websites that sell them.  Is this something that I have to pay for or is it free?

Any advice would be super appreciated.  

Hi, Slopey. Thank you for reaching out. We recommend contacting EASA directly for the rules and regulations of the country you'll be staying in. Here is their contact link:
(https://www.easa.europa.eu/en/contact-us-aviation?select=Aviation). Hopefully, other users from Portugal will give you suggestions too. Safe travels.

Depending on the drone you'll need to register it and label it,   then if it's above 250g you'll also need to do the exam.      You can do this for any EU country and it's applicable to all the others,   I did mine at Alphatango as they also have a good English version.    Also you'll need to check where you can fly as the >250g drones are very limited if they dont have a C1 label.