In about 2010 I had the head gasket replaced an a Ford Fiesta (1.6 Zetec, including grinding). My local garage buy estimated that he could get it done for around £500 (inc VAT) and actually ended up charging me a few pounds under that.
However I was working as a relief van driver at the time, delivering car parts to lots of garages (from the biggest to the smallest) for a Ford main dealer. So, as I was going around, I asked each of the other garages what they might have charged me for the job. The lowest figure I was quoted was £720, with the highest being over £1100 (and most of the estimates being between £800 and £900). So it pays to shop around!