I wrote about the awesomeness of Lego™ before on this very blog. Someone had an even better idea:

  1. Create a 3D model of what you want to create
  2. Replace most of the geometry with Lego™ bricks
  3. Only print the necessary custom parts and leth those have Lego™ knobs at the right positions so that they can be firmly integrated with the Lego™ bricks.
  4. Save a ton of money AND time in the process :)

Luckily, there is a tool that will help you a lot with steps 2 and 3. A great idea!
Watch their video: http://www.youtube.com/watch?v=_bapIwyY7VY
Official project page: faBrickation