I think in American Psycho Bateman and his friends are already super rich before even going into work, having been born into wealth as "trust fund kids". I am pretty sure, unless I remember incorrectly, that Pearce & Pearce, the firm they all work for, is part-owned by Bateman's father, or he at least had the connections to get him the job there? They all have a Vice President title too, so it seems like in that instance they are all just given cushy jobs with nepotism.