For participating in a MOOC you can get different certificates. You can get a Statement of Participation and a Certificate of Accomplishment. The pricing for the certificates is always the same. A Statement of Participation costs 29€ and a Certificate of Accomplishment costs 49€. For more Information about the certificates click here.
If you want to get a certificate for your participation, you can upgrade you membership at anytime. You just have to click on the red "upgrade" button on the navigation bar in your course.
Please keep in mind, that you have to buy the upgrade for the Certificate of Accomplishment at least one day before the start of the exam period, if you want to participate in the exam.