Hi Minikeefy,
Car cost £247 + £178 couple back in August 2011,
Car goes from Paris: Gare de Bercy, passengers from Gare d` Austerlitz which is a short walk (10 min) train was overnight to Nice, prices obviously depend on dates etc.
you can check details here: http://www.raileurope.co.uk/Default.aspx?tabid=2025

we really enjoyed the trip and the train journey was 1 of the comprimises I had to make for `her indoors` due to the distance of the whole journey, hope this helps
regards
Dave