You can save a nice chunk of money if you sign up for a year or more of dedicated hosting at a time. For example, you can rent a GoDaddy dedicated server for $129 per month, but if you commit to a 12-month contract, the price drops to $79.99 per month. Chances are, if you're serious enough about your site that you think it needs a dedicated host, you're probably planning for it to be up for a year. Of course, that's where the money-back guarantees come in, and some sites definitely offer more than others in that regard, so do your research. All our web-hosting reviews cover these guarantees.
Also, if your site uses more bandwidth than you’ve subscribed for, they’ll charge you for overuse. But so do most other providers. Therefore, it’s always good to keep accurate estimates of the traffic on your site. Bandwidth is not directly correlated to traffic, it depends on the simplicity and usage of your site. A simple website with 2-3 pages and with approximately 1000 visitors/mo would need around 1GB of bandwidth.