As standard on Fords up to 2004 you could add new keys yourself if in posession of two programmed keys.
As you only have one working key any new ones need to be programmed to the car using IDS.
Ford can charge stupid amounts and also have the tendency of insisting on a diagnostic check being carried out as well which can be about £80 extra.
My personal recommendation is to source a new unprogrammed key off eBay and call a couple of Auto Locksmiths in your area for a quote.
I added a flip key to my car for £60 (key from eBay and cutting/coding) although that was mates rates from a guy that I have recommended to a fair few people in my area.