Open Source (for humans) - in my opinion - is not about saving anyones money. Its about maintaining a culture of transparency, collaboration, empowerment and freedom.
Running computer systems, in any form, comes with a cost - be it your time or your money - its equally true.
Its true also, that if you don’t care - you are still free (under the four freedoms of foss) to USE the software as you please. However, if you think that running/modifying the software comes without cost, you need to rethink. Free and Open Source Software has nothing to do with cost. Its about what principles the software operates under. In FOSS software, those principles are “hacked” into western copyright law by utilizing a license scheme that guarantee the four freedoms for anyone and mandates that this freedom is passed forward. Its popularly called “copyleft”, but its really just a hack of the existing anglosaxian copyright. As curiosa on this is that it was not until this year that the chines law recognized open source licenses as valid at all under Chinese law which tells a story about the current copyright legislation and its reach.