well as i said for the engine and associated wiring i paid £570 delivered (although i've since discovered the engine is missing its starter motor and AFM but that was the guy being a ****)
The flywheel and clutch depends on which route you take, finding a used one is probably the cheapest option but they're rare, aftermarket solid is probably cheaper than an S8 one from audi so thats probably the way to go, iirc siena was talking about 250-300ish for one, then clutch on top.
Mounts ive no idea, again a scrap V8C5 is your best/cheapest option, no idea how much audi would want for them
Byzan A4 did the 6speed tranny swap into his 1.8T so he might be able to give you an idea of the costs involved with that aspect of it
I recon if you buy wisely and do the spannering yourself, you could have it installed and running for around £1500
If you think about that though, thats 300hp and V8 soundtrack, for much the same cost as a turbo, remap and intercooler for a 1.8T, and the 1.8t wouldnt be making anywhere near 300hp!