To get a reasonable 200bhp from a pd130/pd150 you will be looking at a lot of work. You will need every single fitting from the donor car in terms of wiring. That means the wiring from the engine bay and the interior as that's what the ignition barrel & dashpod attach to (and the ECU in the engine bay).

Essentially you need to rebuild the "brains" of the PD150 into the Golf - total strip down and rebuild job. You will probably need the fuel tank/pump too as that's likely to be different. Matching the driveshafts to the Mk3 could be fun due to differing wheel track (might be lucky) Then there's modding the engine to 200hp (which isn't too hard really)

As a guess, if I had to put a price on a complete PD swap into a Mk3 (or any other car really) I would say you'd be looking at around £6,000. Roughly this is about £2,500 for a low miler PD engine, and all the spares you might need (you might get lucky and be able to buy a complete unstripped wreck for £1500), £3,000 for labour/research/time, etc, and £500 for a custom remap at the end of it all (once it's running fine)

Personally, I would go out and find a high miler PD100 for around £3,000 perhaps, and spend £2,500 odd on uprated turbo and some other bits for a much better 180 to 200bhp.

BTW - This is coming from someone who converted their pd100 to pd130 recently. I'm one person who does know exactly where they're coming from.