It all depends on what your going to put into the box. If you use default powersupply than your going to need to use an inverter (which would be cheaper, but others say it creates noise).
You could go to http://carpc.kyferez.com/ and under tools use the power supply calculator. This will tell you if you can get an opus 150 or if you will need to use a couple of dc to dc power supply's. I am useing the same case for my 2nd system that will be going in my 1996 Baja Outlaw.
Oh by the way, newegg.com has that case for about 20 bucks cheaper.