The front is pretty cute tbh.
I'd expect like, $40. $55 is a bit much but still what I would call reasonable. T-shirts at the store are cheap because of economies of scale... the factories make thousands of shirts and send them worldwide, so the marginal cost of each shirt is small. For smaller and indie retailers, especially for limited-time distribution items, the cost to produce per unit can increase quite dramatically.
I think the cost is high is because Square-Enix isn't expecting high sales for the shirt, so they can't capitalize on economies of scale. This is why Limited Edition goods in general can be very expensive. (Which is justified to the consumer as "this item is rare and valuable and special!!")
Maybe if the shirt enters the regular inventory like the Mithkabob shirt (only $27.99) the price will drop, as evidenced here:
I paid $40 for that stupid Mithkabob shirt hoping it'd get them to bring over the WHM hoodie, but instead we get this
At any rate I'm not preordering the Windurst shirt.
If it was Bastok, though...