Putting a cost on software is adding a restriction, thus making it less free (as in freedom).

Don't confuse "free from cost" with "free from restrictions".

Writing software costs costs - be them time, money, evne mental health as we have often seen because of too many entitled people in these communities. Putting a price on the software means valuing it for what it is, and does not incur in any additional restriction on the usage of the software.

All that said, I think the cost of free software, at least when it comes to infrastructure software, is something that shouldn't be necessary for the end user to pay. Similar to how we pay taxes, instead of paying for the installation of semaphores on our streets directly.

If I were to design any such global system, it would be eg.: distro maintainers who would pay a maintenance cost to the developers of the dependencies they ship. Probably in the form of a funding pool that is distributed across projects prioritizing those that 1.- have ethics and development practices more similar to the distro's and 2.- are in need of more immediate attention for solving security or usability bugs.

Furthermore, national-level funds for this would be collected via a taxation system managed by an academic office or other such entity and taken in a measure scaled according to the nation's average technological "estate" (after all, developing and maintaining a more complex system requires more cares and attentions).