A floor screed is usually a cementitious material made from a 1:3 or 1:4.5 ratio of cement to sharp sand. It may be applied onto either a solid in-situ concrete ground floor slab or onto a precast concrete floor unit.
For example 64 sq metres of 20cm of this R6.45 (per 20cm) would be 817 euros.
Another good video on how to insulate the floor below. Has key details of where to put a vapour barrier – GRADE -> Gravel (with drainage) -> EPS foam -> Vapour barrier (also holds the foam down before 4″ of concrete is poured – > Concrete
Thin sand blinding to level ->appropriate damp proof membrane (well lapped and folded), should lap high enough to connect with, or form, the wall damp proof course -> eps at least 2cm thick vertical around perimeter, top should be level with top of the floor screed (damp proof course), layer and overlap eps -> overlap eps boards with polythene sheet (as a vapour control layer), make sure polythene sheet has 150 mm overlap