Outer Limits 4x4 Board

I am not familiar with Vitaras but my brother has a 1988 Vitara with a noisy gearbox (170k). I am told that this is common in the Suzukis. He has been to two mechanics -one has qoted $2000 and another $1000. I happened to discuss this with an owner from Mount Gambier who had his done for $500.
For those with the experience what is the most likely problem - my brother says it sounds like it is running with straight cut gears and for the given cause offered what would need to be done and approximate costs and options. Are import gearboxes available or reco boxes? I would also expect to have to do the clutch at the same time. We live in Latrobe Valley so if anyone could recommend a nearby reputible repairer/supplier or even as far as East suburbs of Melbourne would be appreciated.

Can anybody point me in the right direction?

When was the fluid last changed?

Fair question.
Don't even know if he has checked his fluid levels.
Although he has had a couple of mechanics have a quick look and I would normally expect he would check those items first.