How much for a tatty S1

[Spiderman]

A mate of mine has an S1 on an E plate,Ash green with tan interior that is currently garaged and not been run for about 6 months.Prior to that it was used daily and has about 90,000 miles on it.
The interior is really tatty,needing a complete retrim,carpets etc.It could do with a respray too,but mechanically it is pretty sound,has recent tyres and steering rack,etc.
How much is it worth?
I was considering making him an offer and using it as a track day car.