"How much is this coin worth" is a common question that this and other coin web site receive.  This question can be difficult to answer without detailed information.  It is very similar to asking someone what a car is worth.  To answer the question of how much a car is worth, one would probably ask "what brand is it", "what year is it", "what condition is it", etc.

In order to answer the question of how much a particular coin of Severus Alexander or any other emperor is worth, you need to answer a variety of questions including:

With these three key pieces of information, one can get a ball park idea of price.  There are a variety of sources that we can get a good idea of the value of the coin.  A few of the sources include coin references, web sites, auction catalogs, and personal opinions.  

Many references include a listing of values for the coins.  Unfortunately many references are old and their prices can be quite out of date.  I would highly recommend David Vagi's Coinage and History of the Roman Empire that was published in 2000.  It has very good ball park figures for coins of Severus Alexander and other emperors.  Also David Sear's new Millennium Edition of  Roman Coins and Their Values offers great information.  If you need information on Severus Alexander, you will need the soon to be released second volume.

Another great place to look is web sites that sell coins.  Ebay, Yahoo, and many of the ancient coin dealer's web sites list past sales of coins and their prices.  This can be a great way to find what someone is willing to pay for your coin.  It helps to have the coin referenced before looking at web sites for prices. 

Auction catalogs of ancient coins is another great place to look.  They list the coins and their estimated value.  It is good to follow up to see what a coin actually sold for.  Many dealers provide this information and some auction guides actually list all the prices coins sold for in a particular year.  

Personal opinions can also be helpful.  Be careful to find someone who knows ancient coins and isn't in a position to benefit from misinforming you.  Always get multiple opinions.  I will be glad to give you my opinion on an Imperial coin of Severus Alexander and tell you what I think it is worth.  By no means am I am professional coin grader or coin expert though.  If you need an professional expert opinion, you should check out David Sear's appraisal service. 

With all of that aside, here is how much you might pay for the more common coins of Severus Alexander.  These are just my ball park figures for overall categories. Rare coins can demand many times the listed prices.   These values come from a combination of David Vagi's book, RSC, auction catalogs, and my own observations.  I am not an expert.  For specific values on a particular coin, check current auction catalogs or have it professionally appraised.

Not liable for use of these numbers.