You won't get much change from £500 for the whole job including materials. You might get it done cheaper, could be more expensive depending on the electrician/materials used. You could find an electrician to quote for it, that's the trade that could do the whole job.
righto.
cost of "getting someone" to do the job (with parts etc)
vs
cost of a shit hot dehumidifier and having ceiling replastered and strange shelf thing in there levelled out. and using window plus bleach.