Pricing for sending out bulk invites is based on individual deployments. A deployment can contain as many customers as you want in each deployment.
With our starter plan, for example, you can bulk invite as many customers as you want in a single deployment for $10. So if you decided to send to all customers who don’t have accounts in your store, that would be $10.
If you decided you wanted to segment your customers into 2 groups, for example, so that you can change the content of the invite to cater to each group, then that would result in 2 deployments (one to each group), and thus would be $20 ($10×2).