Lately there have been a few threads here about trying to start inexpensive nano reefs. Here's an example of a beautiful tank, done cheaply (it's all relative), and featured in Advanced Aquarist Magazine online. It cost less than $400, but he also used frags from his larger system.
http://www.advancedaquarist.com/issues/sept2004/aquarium.htm
http://www.advancedaquarist.com/issues/sept2004/aquarium.htm
with the 100$ light