As long as you follow the GPL license you can redistribute it, for free or at cost. Linux is mostly free as in freedom and usually free as in free beer.
Wikipedia says ElementaryOS has a pay what you want model. So if your image is from them then you don’t have to pay (a 3rd party is free to charge you for it - bandwidth ain’t free).
If no one discussed the value of software freedom on proprietary platforms then (hopefully) we’d be preaching to the choir here.
Linux has proprietary binary blobs in it. If any part of a software is proprietary then even if most of it is free then why do people not call “Linux” proprietary? Libre Linux removes those blobs.