Pro Site Question

I have a user on my multisite that has their domain mapped to theglobalbulletin.com.

I installed the multi domain plugin so they can have multiple site under this domain (i.e. map.theglobalbulletin, news.theglobalbulletin, etc.)

With the Pro Sites plugin they are paying a yearly fee to host the "theglobalbulletin.com" account. Do they also have to pay for each subsite or does this come free since they already have an account and these are just more domains they are adding to?

Thanks!