After playing FFXIII-2 for a few hours, I still haven't gotten any outfits. I noticed that one's for sale in the PlayStation Store, but I haven't gotten any through gameplay. Can you get any without spending more money? How?
Apart from the preorder bonuses or the purchase of the Nordic edition of the game, there is currently only one free outfit: the Style and Steel outfit for Serah. It can be downloaded from the PSN Store or Xbox Live just like any other DLC and from the game (DLC on main menu).
Outside of that, outfits—like the Coliseum—are purely for paid DLC.
The current outfits for sale are:
Summoner's Garb (Part of the Omega DLC/Pre Order bonus),
Noel Battle Attire (Part of the Omega DLC/Pre Order Bonus), SpaceTime Guardian, N7 Armour, Ezio Auditore and Black Mage Attire
(accurate as of 18th May, subject to edits in future)