Cheaper isn't always less expensive. It is tempting to buy the $100 printer online, but be aware that most of these printers are not serviceable, have shorter life-spans, and a higher cost per page. In most cases, the "inexpensive" printer becomes the most expensive printer.
Wrong size. Volume plays a major role in choosing which printers to put in place. If you choose something too small, the device won't last as long and operating cost will be higher. If you choose something too big, the operating costs will be lower, but you'll pay too much upfront. Each device has a recommended monthly volume and it's important to be in the ballpark of that number.
Optional color printing. Color printing is 7 to 15 times more expensive than black and white. If there isn't a direct need for color, just take away the option.
Not using print-related software. There are several software solutions that help manage all aspects of printing. For example, if color printing is a necessity for your business, there are solutions that will restrict color printing by user, department, and even content. This, and other print controls translates into dollars saved.
Inadequate end-user training. User error accounts for a large portion of printer malfunctions. You can prevent many of these issues with proper training on the user interface, document feeder, and paper drawers.
Going at it alone. If you don't want to worry about all of these things, there are companies who offer this service. It is worth your time and money to reach out to an industry expert for recommendations and ideas.