We need more info whats required!
Oil tank, oil powered boiler, pipework plus rads for a three bedroom house is around £6k
You can buy ready built staircases for around £750, allow £250 to fit unless its awkward.
What about plastering, painting, insulating, etc?
Plywood for flooring is cheap, you could do that yourself.
Allow £2.5k for a bathroom, £750 for a plumber to fit – £300 for tiles and £300 for a tiler
Kitchen say £5k (depends on what you want, but £5 k will get you the appliances as well, allow £1k to fit. Is the electrics in for the kitchen stove etc?