Get as much as you can mate. There's fools out there doing it for as little as £1.60 supply & fix, and guaranteed they will be doing a bad job and missing a coat for that money. If it's a whole house then you should be able to do it on a metre rate. Have you taped before? What's the boarding like? Do they want drywall sealer? These factors all affect the price. If you can get £3-£3.50 supply & fix for taping without the sealer coat, then you should do ok. Materials will cost you 40-50p a square metre. Get extra for beads if you can. I recommend that you either hire or borrow a dryawall sander if you can. It will save a lot of mess and prevent you from looking like a ghost once you've finished.