Ive been keeping an eye on the auctions and AU II or III 4.0 Fairmonts go for about $26,000 - $28,000. Ghias are usually towards the top of the range. I havent seen many V8s so I'm not sure what they are worth.
Have a look at www.pickles.com
They have some fixed price cars for sale prior to the auction and from what I've seen the price they put on them is about $500 - $1000 above what you might expect to pay at auction assuming no one else wants the car. There was an AUIII Ghia with Factory sunroof, VCT engine and satnav with less than 40,000 Km a few weeks ago here in Canberra that was sold prior to auction for $28,500. The vehicles I have been looking at all have less than 40,000 Km on them