It's value depends upon many factors such as its condition, mintmark (if any), country of origin, denomination etc. What country is your coin from, because their were no $20 silver coins made by the US in 2005. If your coin is from the US then it is likely a cassino coin in which case it would only be worth $20. It could also be a token of some sort, if that is the case then its value would depend upon many more factors then those listed above.