You're supposed to raise your Intelligence in class until it's about level 4 or 5 then work out at the gym to raise your strength high enough to get a part time job at the gym and slowly gain money each session, but if you don't mind save scumming, you make faster money by going to the university and meeting one of the teachers that ask you to get her a limited-edition handbag via lottery at the department store. After the scene with her, you can go to the dept. store to claim a free raffle ticket and try save scumming to participate in the raffle with just 1 ticket for 1/10 chance of winning, (maybe save outside the department store to change the rng?) Then immediately scalp it for about 7000 dollars profit (you can even go into the negatives when doing this for the first time)