There are several considerations when having to replace your alternator. New alternators are expensive and in some cases may cost more than your vehicle is worth. Used, rebuilt, and new alternators vary in price significantly. Making the decision can be difficult because there doesn't seem to be a typical life span for an alternator. Alternators can last for 20 years or they may only last for 2. Knowing everything about alternators will help make the right decision, however, the amount of money in your wallet is a very important factor as well. The ultimate goal is to not get stranded on the side of the road because your alternator fails.
Rebuilt alternators are typically ok as long as there is a warranty. You might be surprised to find that the only thing you are buying with a rebuilt alternator is the warranty. The extent of some rebuilt alternators is only a good cleaning of the part, maybe some fresh paint, and this makes it "look" new. If it is found that some of the replaceable components should last the length of the warranty than they may not necessarily be replaced. Some auto parts suppliers have even taken to testing their "rebuilt" alternators before selling them because of the large number of failed units right off the shelf. Typically a rebuilt alternator should have a new bearing, voltage regulator, and brushes. These are the easiest and cheapest components to replace. The result is a much more affordable alternator.
Factory Reconditioned Tools
A used alternator might be an option for you. They are typically the cheapest but also the most unreliable. This is due to the fact that it may have been sitting for an undisclosed period of time. During this time of inactivity, the potential for corrosion is high. The contacts and bearings are first things to suffer because of a static alternator. A component like this may have an unknown amount of mileage. The general consensus is to stay away from a used alternator if it has not been thoroughly inspected and tested.
If you drive an old car that you are barely keeping alive, you will be blown away by the typical price of a new alternator from a dealership. Dealerships sell new alternators that can cost upwards of 0, so finding a new aftermarket alternator with all new components might be the best mix of cost and quality. The beauty of a new aftermarket alternator is that you know you are getting all the components new, they come with competitive warranties, and being direct replacement parts that have to produce the outputs that your vehicle requires. You may even find the option of getting a more powerful alternator which is always good to have especially if you are running high amperage accessories.
After everything is considered, you might come to the conclusion that the dealer recommended alternator might get you the most reliable part. Is the extra cost worth it? That is your decision- if you are looking for my opinion, the answer is probably not. I would choose an aftermarket alternator as the best combination of price and reliability.