Assuming you have Marina unlocked then ask her for office work in the morning. Otherwise hope you like washing dishes at home. As far as I know those are the only two ways to grind money.
i found this by total chance but near the start of the game when your in map mode, there's a chance you can find a briefcase with 5000 dollars in it. you can find it under some trees near your home. I'm still using it now.
