The value of collectible coins is affected by material, condition and supply and demand. Other factors influence the value as well, such as the design, coloring and markings.
Coins have inherent value based on the material. Silver, platinum and gold coins have a bullion or melt value based on the current spot price of the metal. Each of these precious metals are traded by investors and have a spot price that is updated daily based on trading. Even if a coin made of precious metal is common and not highly in demand, it is often worth more than face value.
Coins in good condition are typically worth more to collectors than those in poor condition. Collectors prefer the coins to be in the best condition possible. However, some coins are so rare that they are valuable regardless of the condition.
The supply also affects the price. The most valuable coins typically have very few examples remaining that are available for sale. Coins with a low mintage are often worth more as well. However many people collected coins in the United States from the 1930 to 1950s, there are many examples of uncirculated coins in mint condition from this time period. Even with a low mintage, these coins are so common they are not much more valuable than face value or spot price. If the demand is greater than the supply, the coins are worth more than they might be based on other factors.
Other various factors can affect the value as well. Particular designs, colorings and markings can make them more desirable and valuable to collectors. Sometimes mints make mistakes during the striking process, and these coins are typically worth more.