If you don't want to cheat the main way is two jobs - doing a striptease in the Gentlemen's Club in lower New Ark (if you get the sexy fever and have another dancer "make a suggestion" this is REAL lucrative) or work at Roxie's Diner in New Ark proper 4x a day. It won't take terribly long either way - maybe 30 minutes if the RNG gods dislike you.