Is it possible to require payment for an event before allowing a volunteer to register?
CERVIS does allow for a "Paid Event" opportunity type which uses a PayPal Business account to process payments and requires the volunteer to pay prior to completing event registration. There is a $200 annual fee to use Paid events in your CERVIS system.
If you would like to have this feature enabled for your account, please open a support ticket by following the instructions in the Knowledge Base Article found HERE. Once you have Paid Events enabled in your account, you will need to set-up your CERVIS account and your payment account to work together by following the steps HERE.