If they recorded the avengers in London, I can assur you that they weren't hired "under the table", or "on the cheap".  Do you think people like Derek Watkins, or  any of the top level London studio musicians, work cheaply?  That's even libellous to say that.  Unfortunately it's offer and demand, free market etc.  Had they gone to a European orchestra that play for very little money, then you would understand it, but don't try to compare the London session musicians or orchestras to them by any means.  Star Wars, James BOnd and a looooong list of top films have been recorded in England.