Thanks all for your input. I have looked at a lot of sites - many of the kits are fibreglass which I'd prefer to avoid. The composite plastics are lighter, more flexible, and according to my paint shop generally fit better. There is an Australian agent for Rieger in Sydney. Side skirts are $1090 and the rear skirt is priced the same. So throw in a quad exhaust system for $2500 plus the paintwork and there won't be much change from $6000. Ooch!
Thanks for your ideas and comments Astra. I'll contact a Rieger agent in the US and see what they can do.