Hopefully after reading this instructable you will be able to take your first step into robotics. Ard-e cost about $90 to $130 depending on how much spare electronics you have lying around. The main costs are:
Arduino Diecimella- $35 https://www.makershed.com/ProductDetails.asp?ProductCode=MKSP1
Bulldozer kit- $31 http://www.tamiyausa.com/product/item.php?product-id=70104
Servo- $10 I got mine at a local hobby store
Worm gear Motor- $12 http://www.tamiyausa.com/product/item.php?product-id=72004
Various other Electronics- around $10 radioshack or digikey.com
Sensors- anywhere from 0 dollars to $28 depending on how many you want and how extensive your pile of junk electronics is
So with spending around $100 you get a remote control robot with a pan and tilt system that could be used to aim a camera, a hacked airsoft gun ( http://inventgeek.com/Projects/Airsoft_Turret_v2/Overview.aspx ) or you could attach a laser to it because thats what you have lying around. If you wanted to be really cruel you could attach a dvd laser to it and burn whatever you wanted ( http://www.youtube.com/watch?v=CgJ0EpxjZBU )
In addition to making the pan and tilt system that is remote controlled you can also buy about three dollars worth of chips, attach sensors to Ard-e and make him fully autonomous. For around a hundred dollars you can build your own robotics system that has most of the functionality of a roomba or a lego-mindstorms robot: It can sense when it bumps into something be programmed to avoid what it bumps into, it can follow the brightest light, smell pollutants, hear sounds, know precisely how far it has gone, and be controlled by an old recycled remote control. All of this for about half of the price of commercial units.
This is my entry into the RobotGames robot contest so if you like it make sure to vote for it!
Note- Originally I was going to enter the remote controlled version only as my entry to the contest but since the deadline was pushed back Im gonna show you how to make Ard-e run himself.
So on to how to build Ard-e