Hi, sorry to bump into the thread from the middle of no where, but I'm looking for an answer to the same problem. I'm thinking inverters from car batteries are the way to go, heres one for sale on ebay for $31...
http://cgi.ebay.com.au/Car-DC-12V-to...d=p3286.c0.m14
It seems so much cheaper than than the Jaycar unit linked previously, has anyone had a go with one of these?