Hello,
I don't think there's a cookie cutter answer for this. There isn't a policy that deals with this situation directly. Speaking as a host, I would say that it was your fault that you lost the keys and should probably pay the fee. However, if you feel differently, perhaps contact the host and see if they would be willing to reimburse you for some or all of the costs. It probably would have been better to contact them before the work was done and had them agree to pay some or all of the fee before the work was done.
If you aren't happy with the host's response, you could contact Airbnb support directly and explain the situation to them and see what they say. Airbnb generally sides more with the guest than the host, but I'm really not sure what their reponse would be in this case, as the fee was a direct result of you losing the keys.
Best of luck,
Alexandra