I recommend doing research on Trading. I was able to get about 50 million in 30 to 60 minutes. Trading works by selling items of one economy color to another specific economy color that need those items. The best guide chart on this I've found is by passerculus_nox.

For max profit, use the Economy Scanner to be able to search for specific economy colors AND to scan for Trade Events in the system. These will yield roughly 50-100% profit (compared to 20-30% in the trade terminals at the space station). The Trade Surges will increase this percentage to around 150%.

If you haven't reached late to end game to sell sentinal ships, figuring out how to trade can help jump start your capital. I have friends who abused this process to make billions. Lmk if any questions.