Have you considered SouthWest, midway is their hub and they're usually pretty cheap?
If you're adventurous enough, getting to the school from midway would only be $2 by taking the el (subway train thing...) and thats only one transfer and there is a station a short block away from school. I think it takes about 30 min. But only consider taking the train if you're arriving during the day.
Otherwise, by cab, it could really vary depending on traffic, but it would certainly be cheaper to go by cab from midway than o'hare.