Answering OP's original question, as a few of you have digressed from, I would pay the employers the handsome fee of -£3000, this takes into account the cost of travelling, rent and food, etc.
Under no circumstances will I ever pay to do a job that won't get my name anywhere significant for not being stupid. If it was ground-breaking Nobel prize research project where I can reputation or valuable experience that can give me my money back, then it would be a different kettle of fish.
Otherwise, tell those stuck-up arses to stick their much needed £800 where the Sun doesn't shine.