SpaceX has already reused some Falcons 16 times. They're aiming for 20 and Elon, being Elon, thinks they can do 100x. At this point, the biggest expense will be fuel.
All I know if is the one tweet from musk years ago that said 90% savings. But ... musk tweets a lot of bullshit so idk
There's no way they're stripping the whole thing down and replacing 30% of parts in that short of a timeframe. Especially given they do it in Florida, and don't bring them back to the factory. So it's hard to say for sure, but the time can give us some sense of what they must be doing.
And it undercut its sellers <https://www.npr.org/2023/10/11/1204264632/amazon-sellers-pri...>
https://arstechnica.com/space/2023/11/a-historic-falcon-9-is...