When writing a thank you note for a monetary gift, you should mention the amount of the gift and how the money will be used.
For example: Your gift of $25.00 will be used toward the purchase of a new computer for school.
If you don’t have a specific purchase to apply the money to, let the giver know how you intend to use it.
For example: Your gift of $25.00 is going directly into my savings account to help with college expenses next year.