Basement

Despite being instructed to to keep as many bases as you can, do not do it! Soon the two gangs will send a lot of soldiers everywhere and it's pretty hard to gather all the money you need to this achievemente while moving your soldiers around.

At the beginning of the level, send all your employees to the old gym, as this is the only really safe place.

After taking over the gym, sell whatever you can from the other locations. Leave to sell the shelves that still have drugs and at least one of the two vehicles last, so that you don't needlessly waste any resources.

Fire all your employees except one salesperson.

In this new base you can left two employees selling drugs and one making purple + an infirmary (occasionally a customer might get aggressive and maybe attack the vendors, or the purple drug station might explode, so... keep this room) + a locker for three employees. Place cash lockers in all other rooms.

Every two days the police officer will ask for $2.000, but in the fourth or fifth request you might say you don't have enough money and he will only charge $420.

Always send the police attack the stronger gang to balance the game. Once you've collected the necessary amount of money it will be reasonably easy to get all the other bases back. Just hire a lot of tugs and finish the level.