A friend of mine lost a key while being in a different country. She could simply make a copy and it didn't cost much. But the landlord was very understanding.

If you have to pay for the whole procedure and replace the key from your flat and the front door then do not agree on the key service provider that your landlord offers to you. Go to your local key replacement service and ask them for an estimate. When we lost a key our agency was asking for 800 CHF for replacement. But we went to the local service provider and got it done for 400 CHF.