Replacement Value on an Island

[uschisk]

We have a camp on Mark, and our insurance reached out to say their replacement value calculator does not adjust for the cost of doing the work on an island. I have no idea how to adjust the replacement value to closer to what it would cost on the island - looking for advice. Are there insurance companies that have a better handle on this ? Or is there a good rule of thumb for increased cost to move materials on/off and build on the island?

Thank you