How to get cost price?

Excuse me, could you elaborate on how one might obtain the cost price of a cryptocurrency or financial asset? Is there a specific formula or methodology that is commonly used to determine this? Are there any factors that need to be taken into consideration when calculating the cost price, such as transaction fees, market volatility, or the original purchase price? I'm particularly interested in understanding the process of determining the cost price for investment and tax reporting purposes. Could you provide some insight into this process?