three colours were standard black, red and white - so these tend to be the more common. However I would say be openminded on the colour, I have had three corker g40s and blow me they have all been red (my most hated of colours) but I've learned to live with it!
They are pretty similar to other vws of the era - so watch out for rust (round windscreen, on sills, bottom of doors etc) most parts are similar to other polos of the era so are cheap enough. The superchargers do need a service from approx 70k then every 30-40k on a normal pulley but less on a smaller pulley.
They aint that strong so the chassis legs can crack especially if they have had a decent bump - so watch out for that.
Sometimes you get what you pay for - so £1200 conversion seems cheap but may cost you more getting it how you want compared to say a £2500 standard car.