It's not that complicated. You just need to run through some scenarios yourself and use an online calculator, making sure you get your figures correct.
This one gets reasonably close (for me anyway) and will give you an idea:
http://www.fleetplus.com.au/client_centre_calculators
If you do 25k kms a year FBT is 11% on the value of the car (assume 0% business use).
I'm going through the same thing now, selecting the right car is the annoying thing though.
If you don't earn the money or do the kms, it can be expensive.