Not sure where you are in the game’s progression, like you’re at the credit crunch stage of the game. Everybody went (or will go) through it, usually it’s because you’re trying to spread yourself too thin. Best way to keep costs down is focus on one goal and finish that, then move on to the next. Other than Credit Heists, most of the credits you earn in-game are minimal. Once you get a few good teams set up, like 2 or 3, your credits will start building.