You are probably talking about the best part of 7k
4k on a good carpet cleaning machine and equipment, Prochem steampro 2000 or a Ninja from Ashbys are a good start.
Then anything between 2 & 4k for a reliable second hand van, you can always lease a new van but remember that the 1st year is always the toughest.
But all this is useless unless you have the proper training and of course the work!!
Hope this gives you a small insight into the initial start up cost.