I suppose a depth of about 3 or 4 inches would be enough, its basically a slab of concrete off the gable end of a shed, play area/'alley'. Plenty of room for barrows, the actual barrows and manpower would be more the problem.
The only other thing is, I suppose, time. If I could only muster 1 other lad and a barrow, would I have a majorly annoyed driver ? There would be a bit of a draw, say 20Mtrs at least.
The few extra quid wouldnt bother me too much if it wasnt totally OTT, and if it would be easily manageable/practical for a novice.