I don't know too much about laptops, but I know that hospitals throw out or give away their computers every so often. A place of business that uses a lot of computers will always be getting rid of their old computers, usually nothing is wrong with them other than the power supply or the hard drive. Obviously the more computers one business has, the more of a chance that they'll be moving their old computers out and their new computers in.
They may not have hard drives, but everything else is good to go. A friend of mine has gotten several from his locale hospital and added the HD's, he's planning to sell them for $50-$100 a piece.
You may get lucky and find a laptop in a throw out, with simple fixes it can turn out great. Keep in mind that its a good idea to be friends with the head janitor, buy him a case of beer to get on his good side and he'll look out for computers for you. Smooth way to build your money up to buy a laptop, or just make some cash.
Other than that, you can possibly get your laptop/desktop for free.