Q: How much to replace an alternator

Hello. The symptoms you describe are more commonly associated with a bad battery. If a battery is old or worn it may not be able to hold a charge, which will result in a no start condition once the battery runs low. This is magnified in cold weather, where temperature plays a role in the amount of effort required to start the engine. Similar symptoms can be caused by a faulty alternator as well, though I would start by verifying that the battery is in good condition before deciding to replace the alternator. If you are unsure I would recommend having a professional technician, such as one from YourMechanic, come to your location to diagnose the exact cause of the no start condition.