Google Sites is free to use, to a certain extent. You won't be charged for additional features or support, as with other site builders, but you'll be charged once you reach your designated storage limit. And you'll have to pay for your domain if you decide not to use the one assigned to you by Google Sites. People outside your company can access your site, even without a Google Workspace account.
You can also choose to restrict access using the sharing settings. Best of all, Google Sites is completely free to use. No monthly fees, no hidden pricing options, nothing: all you need to do is sign in with your Google Account and you can start creating your page in no time. However, you can buy a domain name and “point” it to your Google site so that you have a recognizable custom domain.