For me, the cost of endgame, fully-engineered ships like the Corvette or Cutter seem to be about a billion and the rank/rep grinds to reach them should be a long-term goal. I can make half a billion in an evening after work if I want, via deep core mining or passenger missions which makes the purchase cost of the endgame ships nonsensical.
Either the ship prices or the income needs to change, because there's no feeling of progression or accomplishment if you can jump straight to endgame ships on day one.
Assuming the ship prices don't change, my feeling is that you should probably be playing for
at least 50 hours to buy an endgame A-rated ship which means that 20M/hour should be seen as the upper limit on any form of credit earning. An Anaconda is, from
Li Yong-Rui space, just 125M credits, and even at 20M/hour - that's something that can be still attained on day one, so no, I don't think 20M/hour is unreasonable. Perhaps it should be considerably lower than that even.
The only thing that needs money is Carriers, and they've been designed as money-sinks on purpose. You only buy one if you have money to burn and nothing else to do with the money.