That's ridiculous price if you ask me.
Have a look at morris 4x4 for the gears, then you should be looking around $400 a diff in labor to have them changed over, admittedly the AUD has died over the last few months which always ups the cost.
Make sure you grab some inner axle seals while you are there buying parts, I would also suggest a rebuild kit for the diffs as well and do all the bearings and seals while the thing is open, will only add around $100 a diff