Option fee appropriate for my scenario?

[Andrew Klein]

I have a property I am trying to sell and the buyers want to close 6 months from now when they are good and ready to move in and would like to keep their inspection contingency until then in case there is any spring water damage or something else happens between now and then. This is a long time to have the property off market while I am trying to sell it and I think an option fee would be appropriate in this situation. If the ask price is $135k, what should I charge?