Hi Marcos,
For more information about becoming Mendix Rapid Application Developer certified, please check the following links:
Regarding the pricing, I tried to sign up for the training and the price it said is € 300,00 (excl. VAT) or $ 400,00 (excl. VAT) or £ 200,00 (excl. VAT).
Good luck!
EDIT: You can sign up here: https://academy.mendix.com/link/onlineexam. Updated the price.
EDIT 2: Updated the links
I also would appreciate from someone in the know about the pricing of the exam. I was under the impression it was free to take, but I can't seem to find any documentation to this effect, nether can I find anything in relation to price.
Thanks in advance.