The shop are a bunch of cowboys who haven't got a clue what they are doing apart from ripping people off. Show them this and say I said so.
Anyway, there are loads of videos on YouTube and information on the internet on how to change the screen. Believe me it really is an easy swap. Get yourself a good aftermarket screen (not the ones the cowboys use) and fit it yourself. Probably 100% better and cheaper than the lone ranger and tonto ripped you off with.
Good luck