For a newborn, figure at least 12 a day. As they get older, less. My one year old goes through about 7 a day. In fact, the companies seem to design the box so that it lasts exactly one week. Of course, you can save by buying in bulk at a big-box store. You can also save by buying online at vendors with free shipping. But, I would say ~$25 per week, since that is the cost of the “week-size” box in my area. Maybe less where you live (I live in San Francisco).