I believe a lot of the cost was because a second track (with all the appropriate signalling and pointwork and such) needed to be put in. Now that the line is probably being partially dualled anyway because of the electric spine, plans will probably change.
But if the site requires lifts and footbridges, access roads etc etc, it could easily be a factor of 3 or 4 times some of the others, of which at least one is a single track station.