Expect pricing to follow weight rather than area, because that is how disposal facilities charge. Concrete is heavy, so a modest-looking slab can be several tonnes, and the number of truck movements usually matters more to the final figure than the square metres involved. Larger volumes generally cost less per tonne, since setup and mobilisation get spread across a full load rather than a part-loaded trip.
Access does the rest of the deciding. Where a truck can back in close to the material, loading is quick; where it has to be barrowed down a side path first, the labour goes up accordingly. On the tight blocks through Cooks Hill, Carrington, Islington and Wickham that is frequently the single biggest cost in the job.
Give us the rough area and thickness, what else has ended up in the pile and how a truck gets to it, and we can quote a fixed figure rather than a per-tonne estimate.