how much should an alternator cost to replace it at a service center?

Hi, are you certain the alternator and charging system in general is not working? Or is it possible the battery itself is not capable of handling a charge? Testing should be performed on the battery first to see if it is the source of the problem. If in fact it tests good and has ample ability to hold a charge and sustain a load, then troubleshooting should go further to check the charging system, including the output of the alternator in voltage and amperage.