Did you find the page about pricing here: https://www.mendix.com/pricing/?
And did you see the part about Does your pricing scale down as number of app users increases?
And the basic plan starts at €52,50/month for up to 5 users, plus €10,50 per user, per application, per month.
But for the details use the form on this page to contact an account advisor from Mendix. He can talk you through the details.
Regards,
Ronald