I would observe that the different methods suggested, except for the one ring for them all and one lighting, the price would vary considerably I imagine and it is because of the methods employed in the different suggestions. So it is very much a case of you get what you pay for. Get a contract listing exactly what is to be done and the costing detailed. Bear in mind many electricians don't plaster or do carpeting and other ancillary work such as moving your possessions around. Ensure they are a member of a CPS scheme and have the correct insurance and that they will issue an electrical installation certificate at the end (EIC) Remember if you decide to change what was agreed it will cost extra!