Floating versions of those machines (dredging vessels) are in the 300M range. And the offshore installation vessel Pioneering Spirit came in at 2.6B: https://en.m.wikipedia.org/wiki/Pioneering_Spirit_(ship)

Fascinating. Had to look it up — the photos of it are mind boggling.

I have to say though, from Wikipedia, sounds like there are only a few of them? Sort of one-offs, each of them (so to speak). I kind of think that might disqualify them.

Like calling the ISS the most expensive machine?

The leaders of the free world sat around a secret table...

https://youtu.be/azEvfD4C6ow

(I know this comment is not exactly in the mood of HN, but this is the one thing I never fail to think of when someone mentions the Bagger family of murderous machines!)