I have read about Powwerline networking where you can use your existing wall outlets to network computers, and is suposably inexpensive:

http://www.howstuffworks.com/power-network1.htm

Here are the advantages of a power-line network:

It's inexpensive. (This author bought a complete Intelogis' PassPort kit to connect two computers for $50.)
It uses existing electrical wiring.
Every room of a typical house has several electrical outlets.
It's easy to install.
A printer, or any other device that doesn't need to be directly connected to a computer, doesn't have to be physically near any of the computers in the network.
It doesn't require that a card be installed in the computer (although there are companies working on PCI-based systems).


You may want to check it out.