Finding a ship that can make good money, and then purchasing the other ships you want in-game is a decent option. The most profitable thing changes from patch to patch, so you can either just keep exchanging your ship for one that can make the most money is an option. Otherwise, just find the role that you can enjoy while grinding. Bounties are always a stable way, but that gameplay loop can get stale real quick (same with bunker missions). Salvaging is good money right now. Pulling cargo off the salvage ships using a freelancer/cutlass/hull-a is pretty decent and a quick source of aUEC. And mining is always an option if you enjoy that. The mining mechanics have improved a lot over the last couple years.

That's how I do it. Grind some cash, expand your fleet and then fly what you enjoy based on what you're trying to do that play-session. You just have to decide which grindy gameplay loop you can stomach to get to that point.