In my experience if you use microsplitters for cleaning upholstery, you get much better results taking more time to agitate making the extraction stage quicker.
The other day i cleaned the seats on Vauxhall Corsa, the seats were really minging!
I wanted to keep the moisture down to a minimum as the custy needed the car in the after noon so i lightly sprayed hot SPM and gently massage the seat with the kestrel, after a short time the cleaning agent plus mechanical agitation had improved the appearance and a low pressure extraction using my CFR tool was all that was required.
Once i had finished the last seat in the car, the first one was almost nearly dry...
Tony - I simply dont have set prices for auto interiors, every car is different so i kind of base my price around my hourly rate... you could probably charge around £30 per seat