There is usually a fee payable on application for a working with children check.
Working with children checks are free for volunteers and foster carers. However, if the person uses the working with children check to work with children other than as a volunteer on 7 or more days of a calendar year, they must pay the prescribed fee within 28 days of commencing work [Child Safety (Prohibited Persons) Act 2016 (SA) s 33A]. It is an offence to breach this requirement, with a maximum fine of $5,000 (expiation fee $315).
For a list of the current fees, visit the Department of Human Services Fees website.