Why would that make us angry?
Anyway, no, you don't have to buy a costume with it. That would be a little silly to wear everyday to school/work/whatever, wouldn't it? You're fine just getting a wig.
As for class caps, I have no idea.
ACen 2014 cosplay: Lara Croft, Erio Touwa, Shirahoshi Hime, Sengoku Nadeko
Otakon 2014 cosplay: Makise Kurisu, Shirahoshi Hime, Sengoku Nadeko
ALA 2015 cosplay: Shirahoshi Hime, Akemi Homura [Haregi ver.], Mayoi Hachikuji
Possible 2015 conventions: Sakura-con, A-Kon