bumpers i would say get from a scrappy,
get them rubbed down and resprayed, i would probably say you get a pair for £50 ish
I think you can buy new g60 arches about £20-25 per arch
G60 steels, i think i seen somewhere you can get them brand set from VW approaching £160.
Koni Red's Golf Mk2 1.3, 1.6 & 1.8 GTI. Excluding GTI 16V Year: 84>90 Lowers: 35-40mm £219.00
Stainless steel exhaust system would vary wildly i would reckon, i would get a GTI manifold put on, then you can have any system made for a gti, much more choice. Not sure on prices, vary wildy upon make, trying to remember the make i always see commended by the GTI owners on here

can't remember,
Clear side repeaters and indicators are buttons, probably £30 for all clear front and sides
Half smokes like 16v lights i assume you mean, seem to be around £50, £70 i think for genuine hella jobs
Remove the side rubbing strips you would be talking quite a bit, would need filling in by a body shop, and resprayed, not cheap
Black badges, cheap as chips.