The basis of the rumor comes from a SE financial report which indicated that Stormblood (which was just refered to as the next expansion at that point) was listed as having a budget of something like 35 million. HW cost 12 million to make. Being unable to read Japanese I cant personally verify if that is true and even then what that 35 Mil is actually spent on is very hard to guess. If they are upgrading all their servers then that might account for quite a bit of the cost.