for the sake of clarification. Users who want to turn away from an odoo SaaS subscription (not matter paid or free [2 users]) to a local server (which might not be on a Enterprise or any other contract) can get this backport service from Odoo S.A., but they have to pay a fee for it, right? Is that a fixed fee? or based on size of the database? Is the exact pricing for that something that can be revealed on this forum?

That's correct. It's a fixed fee in the range of $2000-2500. Contact Odoo sales for confirmation.

I would like to add some clarifications:
- The backporting work is only necessary if the SaaS version is not an LTS version. If it is an LTS version, you can download a backup of your database at anytime and continue locally with a local LTS version (you will just probably want to make sure it's the same build though).
- Backporting is a service that requires about 2 days of work on average (could be more or less) by the Odoo migration team. This is why it comes with a fee. See https://www.odoo.com/blog/5/post/119
- This fee is not mandatory. Just like for everything with Odoo, users have the right to purchase this service or not. Here are a couple alternatives where you won't have to pay this fee:
   a. You can download your database and backport yourself.
   b. You can download your database and install the saas version locally (highly discouraged because you will be stuck in that version forever, and it will be deprecated a couple months later, and it won't even be an LTS version).
   c. You can request a backup of your database from the time it was under an LTS version if that was ever the case (but you will not have the data you have input in Odoo since then).