It used to be possible to make 35m+ in a BB on the BB56 grind. In a CV56 grind, I'm guessing you could make three or four times that much.
Trading crews and selling premium items can easily net someone hundreds of millions of credits. I'm sure there are any number of people that have enough crews sitting in an HQ to make several hundred million credits if they were to sell them.
Personally, I bought 4 BB6s which got rid of most of my money. I got a partial loan for a fifth. And, now, I've already sold all my BB345s with a fleet loan for the last one. I've got 35m right now, but that will be gone within the next month.
I always said this game needed a good credit sink....sucks that I've found that I completely screwed myself from trying to get any crews or items just to have 6 ships.
I guess I need to raise a CV crew.