Open source doesn't even cut costs, because code licenses represent only a tiny portion of a major product's cost.
The chief value of open source is visibility. (These highly visible sneakers cost $120 from Xander. Picture from Hypebeast.)
You can see the code, you can test the code, you can improve the code, but mostly you can see the code.
When you see the code vendors, of necessity, change their business models. Their costs move to the back-end. They look for subscription revenue, for services revenue. They look for ways to help a project work.
When you can see the code you have a different relationship with it. You're no longer asking what it can do. You're asking how you can adapt it to your needs.
With code visibility, you and your vendors become partners in trying to make something work. The vendor can't over-promise, but you can't over-assume either. This may be one of main hidden reasons for IT failure, the two sides of the transaction not being on the same page.
You can also get around a vendor with open source. If the vendor doesn't have time to fix your issue, you pay someone else to fix it. Maybe you hire someone, maybe you just go to the community or its commercial arm. There are no more excuses, well no more you have to tolerate, with open source.
When code is visible, and you're a member of the code community, you're going to be up-to-date on improvements, enhancements, and bug fixes. It's not just that the code becomes visible, but you become visible as a user of the code.
It's true that in the enterprise space there is no such thing as free code. There is only visible code and invisible code. When you have open source you have the visible kind, and this makes all the difference.