At the pittsburgh field, I make just under 2 million per full load of scrap metal that I bring in. It takes roughly 5-10 minutes, depending on if I'm chatting with others nearby or having to deal with oorp attacks, to fill up my cargo hold. At most, that's 24 million per hour, but it averages closer to 15-16 an hour.
My smuggling routes make 25-30 million per hour, take less concentration, and oddly have less risk of attack.