As in software that’s licensed under a open source copyleft license, but costs money to run that’s beyond an optional request for a donation. I can see this happening with libre hardware since it still costs money to manufacture even if the design is free, but with software, wouldn’t someone immediately fork the project to remove the payment requirement?
ElementaryOS is some kind of an example, you can get the source code, but they ask you to pay (it’s not mandatory though and you can get everything for free) to get the ISO file.
Other examples would be Ardour and Fritzing, both have source code available for free, but not their binaries. So if you want to have it for free, you have to pay with time of compiling :p