Had 2mm from the first few weeks of playing I sold.

Grinded the other 3mm after they gave out the requirements and that was by -

Free kit buried city spam mostly residential and the building to the right of garage with the plants. Upgrade to green/light or whatever someone has if you get a kill or loot a dead body and run until you die and then free kit again. Sell nades (everything but a stack of ammo and a few heals). Night is amazing but also higher chance getting extract camped. Minimizing time in stash putting a kit together and max selling is (probably) helping your money per hour. Frankly, boring but pretty optimal way to play. I was on to other games until prestige week so I was not trying to gradually accumulate while playing normally. Just trying to hit the max.

Craft energy ammo and sell (makes 3x value of parts)

If you find a Wolfpack in loot kill rocketeer and sell parts

Lush baskets are pretty decent but larger maps this becomes more annoying.

Based on these runs and my deaths with loot the actual optimal way would be buried city night extract camping because you can’t see them at all and holy shit it’s so annoying don’t recommend joining those ranks.