how do coins get their value

i am always asked by people how do coins get their value. well one starting point is it's not how old the coin is but how many of that type were actually minted. this is an important point for numismatics because some people have approached me about ancient coins and i tell them they are constantly finding them on digs of ancient sites and they are not that uncommon. in comparison a 1922 0ne cent coin is selling for about twenty dollars now because they were minting a great deal of silver coins that year and didn't mint very many other coins. futhermore, only one mint was in operation that year.
the point i am trying to get across is many factors come into play and one of my goals this year is to keep geting out more information like this so my readers will become better informed when in the marketplace.