Yes. You can choose the billing style that suits you from the Packages & Add-ons page, which has two options:
Custom plan (flexible, monthly)
A flexible monthly plan where you choose exactly how many Maildoso (SMTP) mailboxes and domains you want, using the sliders. (Google Workspace mailboxes are currently unavailable for new purchases — see note below.)
Mailboxes are added in bundles (minimum 10 at a time), and the per-mailbox price depends on how many you have in total — larger volumes get a better per-mailbox rate.
On the Custom plan, domains are purchased separately at $12 per domain, per year (a fixed price, with no volume discount).
Packages (quarterly bundles)
Quarterly bundle plans that come at a set size, with domains included in the package.
A good fit if you want a ready-made bundle rather than configuring each item yourself.
Note: New Google Workspace mailbox purchases are paused for the time being. If you already have Google Workspace mailboxes, your existing plan, billing, and support are unaffected — Google Workspace mailboxes continue to be billed monthly as before. You can view current sizes, prices, and add-ons directly on the Packages & Add-ons page. For how mailbox and domain charges appear on your bill, see Understanding your bill: mailbox plans vs. domain charges.