i'm a bachur in yeshiva, and i have limited cash funds. the k'nas should be something that would bother you enough to be a preventive measure not to act out. it shouldn't make you broke, or you'll just end uo dropping the k'nas entirely. as my rebbe told me, and as they said in the Charmin commercials, "Less is more". also, the k'nas doesn't have to be money. it can be to do something you don't really enjoy doing or not to do something you enjoy doing.