You can get general purpose enclosures (project boxes) for hobby electronics in most sizes for much cheaper than building things from LEGO.
Otherwise you can build boxes easily out of balsa wood using only an X-acto knife, a steel rule and a cutting mat (and some glue). They wont be rugged by any stretch, but will be fine for office type environments.
another alternative is building boxes out of plastic sheet and strip stock used for model building. These just require the same tools as balsa boxmaking, and can be made pretty rugged if braced correctly. In addition, plastic enclosures can be sanded and painted to any level of finish you may desire.