Answering this question can be a bit tricky. When answering this question you'll want to show a balance between the two. Steer clear of stating monetary things you've bought with your salary or anything too personal. Tell the interviewer that you enjoy the work and the money is an added bonus.
"Work is more important to me than money. I would rather work in a positive, empowering environment than somewhere I didn't want to be and get paid a little bit more money."