Please tell me do we have to pay 400 aed. before...

You should contact the General Administration of Residence in Ras Al-Khaimah to obtain all the information related to the amounts that must be paid upon departure in addition to determining the airport through which to travel and you can get all the contact information with the General Administration of Residence in Ras Al-Khaimah through the website of the Government of Ras Al-Khaimah through the following link: 
The Government of Ras Al-Khaimah