you might be able to buy the key on ebay,bear in mind you might have a pats chip in it,this will no doubt have to be programed to your vechile,thats the reason ford charge a bloody lot for a simply job,timpsons cut my key ford galaxy for about 8 quid,try them.
just had one for a renault trafic that was £160
but was done free through my insurance and is only the spare second key
so i didn't mind. or i wouldn't of bothered.
£100+ is common for replacing keys from main dealers.
IN a Ford, if you replace a worn key, you can get a simple one cut from a local place & take the old module out of the old key & glue it into the new one.