It depends on how bandwidth intensive your site is. I know of one site that gets around 10,000 uniques per month and uses just under 5GB of bandwidth while another uses 10GB because the site also makes use of Flash animations.
It is important to make a distention between "hits" and "visitors". A hit occurs every time something is loaded. For example, if someone visits a page with 10 images, your stats counter will record 11 hits (one for the page and 10 for the images). The number of hits you get each month doesn't really mean all that much. The prime reason it is so commonly used is because it inflates the popularity of the site in the eyes of people who have limited knowledge of how site statistics work. You should focus on the number on unique visitors you get each month.