Hi there hope i can be of assistance.
£900 from a Ford main dealer sounds about right. The parts alone for the new flyhwheel, clutch and slave cylinder from Ford costs just under £400.
However, if you shop around for an experienced local garage, the labour cost will be lower. A main dealer will charge around £50-£60 per hour. A local garage will be alot less.
The job of removing an replacing the gearbox/flywheel etc shoudl take an experiecned fitter around 5 hours in total, as long as nothing goes wrong, i.e seized in bolt etc which will take extra time.