Hi Mark
Are you sure its all leather?
Very often the vehicle manufacturers only put leather onto the seating areas the rest is coloured vinyl made to match.
Its a long time since I cleaned car seats so my pricing would be well out of date ( a bit like me and sell by dates)
I will hazard a guess it would take a couple of hours or so depending on the amount of soiling. I would be charging my time at least at £35.00 an hour. Check that the seat edges where the driver gets in and out have not lost colour or it may be a re-dying job...more cost involved here.
Hope this helps
Derek