I imagine it will be outrageous, but I do hope they go with the 'tons of fairly normal mats' option instead of 'tons of expensive and heavily restricted mats' option. I guess it depends on what you can do with it. Somewhat paradoxically my instinct as it pertains to SE is that the more useful it is to have an airship the easier and more cost effective it will be. The less useful it is to have an airship the more ridiculous and expensive it will be. I imagine that at minimal use (grants no advantage and other players can't even be made aware that you have one) it burns 1 tier IV materia per second as fuel.