It depends, there are various distribution options depending on the GPL version. You can either distribute the source together at the same price, or you can offer to get the source later from a different medium charging no more than your distribution costs (e.g. cost of physical medium, server hosting costs, shipping costs). That's kind of GPLv2. In GPLv3, it talks about "equivalent access", which I think means you can also charge for the source the same price that you charged for the binary.
It means if you offer the binaries for download it is enough if you also offer the source for download. So you don't have to have a mechanism for distributing physical media.
https://www.gnu.org/licenses/gpl-faq.html#DoesTheGPLAllowMon...
The GPL isn't as anti-commercial as its detractors make it out to be.