The miss could be something simple like a cap/rotor, plug wire, spark plug.
Bad/clogged fuel injector. Faulty wiring somewhere between the ECU and the injector.
Or it could be something more involved like poor compression, cracked intake/exhaust valve, partially blown head gasket etc.
Being that it's auto and has a miss that the owner doesn't seem to care about, I'd think $500-800 depending on the rest of the car & if not then move on