I would just use a strimmer on a lawn that size.
Costs I’d expect to pay.
£200-250 per person per day.
£200-250 per skip.
Mini diggers and small plant are surprisingly very cheap to hire in especially on a week hire rate. A powered wheelbarrow for muck shifting maybe £125 a week.
Plus materials ofc.
Based on your logic of £250 * 3 people per day * 10 days (I think it was longer originally) = £7500. They had 8 muckaways at what I was told is £350-400 per load but even using £250 that's another £2000. Then there's 40sqm of patio at £40 per sqm which is another £1600 taking us to £11,100.
Then there's been the digger, materials for building the wall, split face tiles, topsoil, turf etc etc. At least he saved some money on drainage originally

But the point is I don't think the £14,750 I paid goes very far. He certainly won't be spending the summer in Florida based on what i've paid him.