How do I unlock the additional batsuits in Batman: Arkham City Lockdown?

Batman: Arkham City Lockdown has several additional batsuits available. I've completed all the stages once, and am now going through them again. I expected to unlock one or all of the suits as I progressed, but that hasn't happened. I see that there's a Purchase button next to the suits, but assumed it works like WaynePoints: available for purchase if you don't have the patience to earn them. Do I have to purchase the extra batsuits? Or do they unlock at some point in the game?

I can't find an authoritative source, but several reviews of the game mention the fact that additional Batsuits are paid DLC, whereas the gadget upgrades can be unlocked without having to pay.

Rocksteady did something very similar with Arkham City, so there's precedent for this as well.