Hey
Its does not have to be real expensive, although define "expensive" ?
i got a...
ARY (180bhp ) complete engine minus gearbox for £400 delivered
A3 gearbox £100
Mk2/mk4 spliced loom off of Ebay £80 (kk i was lucky)
K04 complete conversion kit £350
Would have cost me this total for a bare BAM engine. Which ofc would have needed much more spent on it.
Although it does not stop there. You have the questions of, do you do head gasket while its out of the car? not bad if you do yourself, then there's the cam belt/water pump, £100 plus just for parts, again ok if you do yourself.
G60 fly wheel + VR6 clutch ( unless you wanna keep the DMF )
Upgraded brakes you WILL need.
New suspension/sub frame bushes etc..
Do you want more than the 150-180bhp, ofc you will, if not you might as well keep the ABF engine. So that's another few hundred+ for a remap and associated new/upgraded parts.
No point mapping a tired engine or components.
The other thing people forget is TIME. Ive spent over a year sourcing the best parts i could afford ( which is not a lot. Im a working father of two kids and a high maintenance wife

). Most of that year ive been having fun

reading wiring diagrams for the mk2/3 ( as my mk2 has an ABF also ) and mk4 golf and audi TT ( ARY engine is out of a TT ). Oh the joy.
All info is out there on the net, just take your time and look around there's a lot of good people who are willing to help out. Many guides and part lists etc.
Also as your going the k04 route also make sure you get the different turbo bracket, different oil/water pipes, bam injectors charge pipes, I/C. Down pipes seem to be very highly priced also.
The above posts ( a few up ) problems can be alleviated by swapping to hydro clutch with Corrado pedal box and parts and the cam belt cover hitting the MC can be fixed by putting the MC on the off side ( easy move ) or by using a passat diesel rear mount.(easier) Look it up its all out there on the web.
All the best with the transfer mate. Ill be swapping my engine in after Christmas when my job is more quiet. I will try help where i can.
As a side note: I see mk2's on the bay with BAM/BAM spec engines up for 4-5k.

All the best.