how much for break service

You can get a estimate on brake service here https://repairpal.com/estimator/mitsubishi/montero+sport But a shop will have to tell you what exactly needs service, You can locate a shop near you here https://repairpal.com/mitsubishi-repair-in-kansas-city-missouri

check your brake pads and se if they are almost gone. You also might consider spraying it with brake cleaner and see if the noise goes away.