Boss is "requiring" we dress up

I work at a summer camp and next week is decades week. Every day is a different decade. However our boss is saying dress up is mandatory. She's wanting tye dye stouff, bell buttons, poodle skirts etc. Ummm... I'm don't own anything she's wanting for each decade day. And I'm a poor college student. She pays me $10 an hour. I'm not gonna waste money I don't have for something like this. I feel if she wants us to dress up, she should be the one providing the clothes instead of expecting people who she pays $10 an hour to purchase a bunch of stuff they will only wear once.

@Niki we have summer camp tshirts

@L.P.D people have been commenting under the post she made about it and she hasn't replied to any.