Depends who is doing the work and whether you’re prepared/wanting to do some work yourself.
If you’re getting a proper builder in then you should budget £150 – £200 a day for each man.
Taking down the ceiling and [properly] cleaning up will be half a day. Plus waste disposal.
Insulation – assuming there’s ventilation above – is an hours work for mineral wool. 300mm will be needed to comply with current minimum standard. Vapour barrier underneath, then plasterboarding and then a plaster skim are another half day for two men (so a day). Although if you use half sized boards a single man could do this.
Electrics should take half a day. Plus the fittings you’ve choosen. There will be a premium as a contribution to the hole cutter being used.
Two and a half days in total so far. So £500 for labour and then materials.
Assuming the property is in England or Wales then you’ll need Building Regs Approval for the insulation and the electrics.