Just a quick search on google shopping for "power inverter ac to dc" found a whole list of them from about $20.00 on up. http://funadvice.com/r/3kp1mr6c61
Just make sure it has a high enough wattage to power what you need to.
Wal-mart. Wal-mart has everything... and I mean EVERYTHING.
...Plus I've seen them there. Lol.