My newest Picaxe project was to figure out how to use an $8 Picaxe, controlled by a PIR sensor to run a 12V vent motor. With the help of Fritz_42 again, we came up with a easy, low cost solution. It involved using Fritz's VLC (Very Low Cost - http://www.ipprofessional.com.au/VLC...Controller.pdf
) controller which runs less than $10 to build, a Parallax PIR for around $10, a $4 add on board, a $3.50 vent motor (they're still on sale until the 28th - http://www.goldmine-elec-products.co...m_medium=email
)and a battery pack and a 12V power supply from the spare parts box. For under $35 even if you have to buy a cheap 12V power supply, you can have a triggered, fully adjustable prop motor and controller. I don't know how you can beat that bargain!
I know that many people are afraid to get into building their own electronics, but this is a great way to start. It does require some soldering but it's easy to learn.
I hope you give it a try. I have a layout diagram and the program code if anyone is interested.