The cost is in doing all the work in one place.
Doing this install properly isn't cheap.
Using a fitting kit example:
2nd hand Engine and Gearbox and Wiring Loom $2300
Engine Install $450
Fitting Kit$350
Diff $250
+ shortened + modify mounts + respline $600
+install $250
Fuel Lines + EFI Pump + surge tank $300
Clutch pedal parts $150
+install 0.5day$200
Wiring + labour 1day $400
Radiator + Install + labour 0.5 days $550
Piping to intercooler + hoses $500
Move battery to boot $160
Exhaust $250
Stiffer rear springs to deal with axle tramping $180
Bigger brakes on front $350
Booster and Master Cylinder to suit brakes $100
Retractable Seatbelts and passenger mirrors for registration $200
Engineering certificate $300
With all of this and probably 10 hours additional labour @$50/hr $500
AUS$8340. That's even with the savings made by using a fitting kit. Instead spending 10 hours making the engine and gearbox mounts. Which would add another 5-10 hours labour.
I think you might get away with $6000 if you don't mind having very bad brakes. How much is your life worth?
These are all approximates. I sometimes forget how much can be saved by spending days on end searching wrecking yards for cheap parts. This will take even longer if you don't know what to look for. R&D is always where the expense is.
This is why I think that any work on cars 'must' be a hobby that you enjoy. Otherwise you are paying other people for their knowledge, and you risk being labelled a chequebook tuner.

Flame me if you think I'm wrong. I think working on cars, and developing a good set of tools/equipment is critical to doing the job yourself. If you can't invest in tools, then paying someone else is the only alternative.
Chris