Registration exam for a Salesforce Administrator 201 Certification exam costs $200, plus taxes according to your location. If you're unsuccessful at the first time of asking, the fee to retake the Salesforce Admin Certification exam is $100, again plus tax.
If you want to prepare for Salesforce Admin Certification exam, check out this Salesforce Course by Intellipaat.
You can watch this video on Salesforce by Intellipaat to know about Salesforce certification in a detailed manner: