The cost to fix squeaky brakes will depend on what is actually causing the vehicles brakes to squeal.
Brakes squealing can be caused by many things so there's no way to say 100% on what it will cost to get the squeaky brakes fixed.
Cost to fix the squeaky brakes can range from as low as $75.00 to $300.00 though depending on what is causing the squeaking brakes.
Things that can cause brakes to squeal and squeak are worn brake pads, glazed brake pads, worn or warped brake rotors, lack of brake pad insulation, broken anti rattle clips, lack of insulation shims.
Another cause of brakes squealing or brakes squeaking is the wear indicator on the brake pads that is supposed to touch the rotor when the brake pads wear down to an unsafe level.
Either way you should get your vehicle to a brake shop to have the brakes inspected or if you can do it yourself get those brakes fixed as it could lead to a deadly wreck.
Brakes are what stops your vehicle so always get them checked and fixed.