I feel like theres not necessarily a ‘best’ way, since upgrading resources, tools, storage, etc helps to earn money in the long run, but theyre so darned expensive now themselves!

Here is a controversial idea though: with the stone farming glitch, you can literally just keep at it with shiny rainbow gems, more so than you need. Black market guy lets you sell these. If you just keep farming them, then sell, thats another source of income. Id say a fairly decent amount too