College Is Paying Students Less For The Same Jobs They Hire The General Public For, Is This Legal? (illinois)

I go to college in Illinois and happened upon a Facebook post a couple months ago for a modeling job for my college's art department. The link on the post was for the general public, and I applied not knowing that a student job opportunities website even existed for the school. The wage listed on that site was $22/hr.

Flash forward, and I have the interview, finish submitting my identification info, and they agree to hire me. However, I got an email a couple days ago from one of the hiring managers and she said since she noticed I'm a student, I need to reapply through the student job opportunities site. I thought that was kinda weird because they already have all the necessary documents and everything, but whatever. She said she had to have the job reposted on there just for me, so I just went and reapplied and the listed wage was $17/hr instead of the $22.

How is this even legal or fair? Are they allowed to pay students less for being students? It's a nude figure modeling job, and I'm very comfortable in my own body, but I don't think I want to show off everything for only a dollar more an hour than what I make now. I have to go in next week and fill out the rest of whatever documents they need, and I plan on asking for the $22/hr because a whole $5/hr cut is ridiculous and asinine.

Anyway, is there anything I can legally do about this or is this just another way colleges swindle and take advantage of people? If she refuses to give me $22/hr, I'm probably not going to do it.