Lost keys....landlord wants 2700 euros

Dear All,
I lost my appartment keys in a serviced appartment. This key was also used for main door. Hence now the landlord and the agency wants me to pay for changing all the locks in the appartment(as everybody has one key which can open the main door and then their respective appartments). So if the main door lock is changed, everybody will have two keys....and they have sent me a quotation of about 3000 euros....how to deal with this situation?....please please advise and help...