I read an industry article mid-COVID that claimed the biggest barrier to offshore right now was the lack of ships to install them - alleviated somewhat by the introduction of floating offshore rigs, like these:
So yeah, it's gotta be way cheaper to drop a couple of those in the ocean than truck towers out to middle-of-nowheresville or digging a foundation at the bottom of the ocean or whatever.
Interestingly with these size is not the be-all and end-all. If you make them so that they fit in the average port (towed by an average pair of tugs), the range of locations where they can be installed increases a lot. As does the availability of ships usable for the install.
These have been around longer than fossil fuel powered ones. They're called bikes.