A monthly expense would depend on what you are broadcasting. If it is a non-commercial radio station, you will have to figure out where and how your programming will be produced. You may have volunteers, ala Pacifica, or you may pay for programming, ala NPR.   You will have operational expenses such as equipment upkeep, electricity, insurance, staff, etc.    I'm not sure what you mean by "credentialing for staff".

You need to determine what you will be doing with the station to draw up a budget.

Ron