This depends on which service provider you use and whether you want to use your own account or our account.
If you would like to use our account, the video call would go via the platform Zoom. The basic version is free of charge for up to 100 participants. For more than 100 participants up to 500 participants we charge 50 € for the use of the access.
When using your own accounts, you need to check which license you have. Generally, most „basic“ licenses are limited to a certain number of participants.