Alavahalf has asked a few questions on your other thread Tilly.
Anyway, my comments...
When they excavate, are they disposing of the spoil?
This would need either a hardcore or a concrete base.
Are they supplying the slabs?
A circular patio of that size could easily account for half of that quote.
Does the price include VAT (that would account for £200)
Even if not including VAT, that would seem a pretty good quote.
You have other quotes coming. I'm sure that would confirm it.