The regulator I used was an IC from a PSU we had lying around in my office. I would suggest that firstly you decide on the AP/convertor that you are going to use and check its current requirements. There is no reason that you have to have a 12V AP, it is just that this matched the parts I had available and the Intel boots in around 15 seconds as opposed to the Cisco which takes about a minute.

You should then be able to get a regulator from an electronics supplier which will satisfy the device's current and voltage requirements. If you have soldering skills then an IC will cost you around £5, otherwise budget on around £10 for and off the shelf cig. lighter adapter or something and modify it.