sapphire crystal question

[alanmead]

Does anyone know the appoxamate cost of having a sapphire crystal fitted to a Cartier Tank Ameriane?
When i had the crystal replaced before i was not made aware of the options regarding replacing the crystal. They just told me it was £54 and that was that. However they put a mineral crystal on the watch and there are some very small marks on it that just would not be there if a saphire crystal had been fitted.
Thanks for any help.