I've ghosted a few books -- a couple of as-told-to memoirs and some novels where I swore never to reveal that the name on the cover didn't do the work.  I've also sold nineteen novels under my own name and more than seventy short stories and novellas to mass-market magazines.

I've never added it all up, but if I didn't make more from the ghosting than from the ghosting than the straight-up fiction, it was close.  It pays very well.  As Christopher Shulgan says, the trick is to be able to write in different voices.