I think the biggest non-standard cost is obviously transportation of materials to the island, but that can't begin to explain the purchase prices. The last piece of land I saw for sale (big enough to build a villa on) was around 440,000 Euros as I recall. The latest villa to be built (and it may actually be on the land mentioned) is up for sale for 1,000,000 euros. I doubt shipping materials by boat caused that sort of mark up
