Here is a vertical axis windmill that is inexpensive to build and portable!
The sails are sewn from ripstop nylon fabric and the frame of the windmill is built from stuff that you can buy from your local hardware store. Due to the way that the sails move back and forth it can capture the wind more effectively than the traditional firm VAWT designs. It works more like the sails used by wind surfers and sail boats. The sails can flap in higher winds and so I am working on ways to minimize that noise. When perfected it could be a great way to capture wind energy.