It is not possible to determine the average value of a state quarter with a mint error accurately. Each error type and/or individual error is unique with regard to the error's amount of detail, the degree of damage to the coin, and its rarity.
Examples of minting errors that are based on degree or detail of disfigurement include but are not limited to die cracks, rotated dies, off center strikes, broadstrikes and lamination errors. Missing design features are also among these minting errors. In general, coins with striking errors are more rare and thus worth more while coins with die or lamination errors are worth less. Once the coin type, error type and degree of error are determined, the coin collector can more accurately compare the coin to others of its type to calculate a rough average.