There are several ways to deal with it, depending on the business model of your airline. The easiest model with little knowledge is surely the B 787-8.
My longest route is London to Sydney (16000km +), and I use the 787 for this. Do not start any long haul routes until your airline is established and has a complete domestic network. You wont get anywhere near enough PAX, as I suspect my Sydney flight fills up with transfer PAX from all over Europe....
of course, go through the Aircraft Evaluation tool to determine which aircraft is best. Depending on server, you maybe able to get some good discounts for secondhand aircraft, so you need to manually adjust (in your head, ms excel, or paper) the revised capital costs to determine cost per seat.