Hey Nicole,
Just wanted to add my own experience... last year I had three on campus jobs: blogging, tutoring other students in the Writer's Studio and working as an assistant for one of my professors in the English Department. I worked about 3-6 hours in each of these jobs. There are definitely some jobs that offer more hours, but I just preferred to take up a few smaller jobs to keep it interesting.
Also, don't totally dismiss the option of working off-campus (unless you don't have a car.) Butler has job fairs that help you find employment off-campus if that's something you are interested in. My freshman year I worked for a tutoring agency and got to work with students in an inner city high school, which was a really rewarding job and an experience I would not have traded for anything!