Condition: The condition of the coin is one of the most important factors that determines its value. Coins that are in good condition with minimal wear and tear will be worth more than coins that are heavily worn or damaged.
Rarity: The rarity of the coin also plays a role in its value. Coins that are rare or have a low mintage will be worth more than coins that are more common. The 1877 US silver dollar is not considered to be a particularly rare coin, so its value is not as high as some other silver dollars.
Numismatic value: Some coins may have additional numismatic value beyond their bullion value. This can be due to a variety of factors, such as errors or unique characteristics. For example, an 1877 US silver dollar with a mint error could be worth significantly more than a regular 1877 silver dollar.
Overall, the value of an 1877 US silver dollar can vary depending on its condition, rarity, and numismatic value. While the average value is around $20-$30, some coins can be worth much more. If you have an 1877 US silver dollar, it is a good idea to have it appraised by a professional coin dealer to determine its exact value.