To get the list of those users , the monthid between startdate and enddate, you can try something like:
select
Transport_Details.User_Id,
Route_Fee.Fee
from Transport_Details join Route_Fee
on Transport_Details.Bus_Route_Fare_Stage_Id=Route_Fee.Bus_Route_Fare_Stage_Id
where Route_Fee.Month between month(StartDate) and month(EndDate)
not sure whether this will come - Route_Fee.Month=4