Anything you've already paid, or would have paid at the point you needed to cancel. Because they won't give you money you haven't spent.

klm_cip -
You are asked for the trip cost because that is the figure they use when calculating the limits of your coverage and the cost of the policy. You can estimate and include all the costs you anticipate, not only what you have already paid for up front. For example, if you have a hotel reserved but not paid for, you would include that cost. Of course in the event you have to use the coverage, you would be reimbursed only what you had actually paid (e.g., nonrefundable deposits.)