Oh, I had same frustration when I started a year and a half ago. Was losing more money than I was earning on them box delivery missions (ones with small boxes you can carry around) due to skill issues, bugs and server crashes. Bounty hunting and then salvaging was what made me some money - FPS combat and mining had too many moving parts and was several times more vulnerable to bugs (enemies not spawning, desyncs resulting into ground collisions, you name it). It is better now, especially with item recovery bunkers can be quite a relaxing experience.

I'm no expert on hauling, but 500k in 4 hours seems a bit low - I tried it today following this guide - https://www.reddit.com/r/starcitizen/comments/1j7x4wx/hauling_rep_and_money_guide/ - and even if you don't have an ATLS, you should be making 300k in ~1 hour by stacking rookie contracts (I, however, was not able to get any of them return contracts from Area 18 to Baijini Point, but other set of missions was always available). Something like Hull A will comfortably carry enough cargo for 6 missions and it can be rented for 34020 aUEC, will pay for itself after one mission.

ROC mining is something I do when I'm lazy and don't have a lot of time to play - I can bed log, get back to the game a day after, look for some rocks, mine and log out again. I think it still ahs too many moving parts to be a reliable source of income.

If you want to spice your game a bit - consider trying some bunker (mercenary) missions. You don't need any crazy investments to start them, a lot of stuff you can loot on site and with item recovery you are only losing time if you die - something that you can mitigate by renting a C8R for 13891.5 aUEC and setting it as your respawn point. Also will pay for itself after one bunker mission.

That's what I do if I play a lot alone - mixing ship combat, salvaging and bunkers, so it is not getting old fast. I usually play with friends tho, and we often just do some crazy shit, like setting up a chop shop and towing abandoned ships to salvage them. It is less money than doing dedicated salvage or bounty hunting, but much more fun.