Dont know of any Self Employed Decorators that earn £150 per day in this area, We are in a recession the last thing people think about is paying someone to decorate a room,
Mortgage, Food, Heating take priority, Decorating can wait until next year (or the Year after)
Get an Electric Steam Stripper £20/40 and a scraper far cheaper.
(£120-)£150 a day is the going rate in London, for a decent decorator.
Never-the-less you are correct that you could find someone cash-in-hand who will do it for far less. I avoided that recommendation largely because you increase the risk of a wall with the aforementioned gouges.
If the OP is planning to make good & decorate then i too would suggest that they strip the walls themselves. As you said the capital outlay is very small.
£10 per hour is considered good here unless one works for a Contract Firm, these are the only ones that are surviving,
self employed have gone to the wall, no work at all,
a recent build of Apartments was completed and remain empty, the decorating was shelved, and will only be resumed when a Particular Apartment is sold