I would look into the M2-ATX power supply if I were you. It's suppose to deliver 8A on the 12V rail (5A for the Opus). It's also suppose to be 90 bucks plus shipping. The problem is it hasn't been released yet, but is suppose to be on the verge of it. I was told the 15th of this month.
Between you and I.... you could probably get away with 5A, if you are able to underclock and undervolt the Celeron sufficiently. But you will be cutting it close. You have to share the 12V with the Xenarc and hard drive, as well as any other 12V devices you might pick up down the road.