Definitely buy your tickets at the box office (around the corner from the main entrance on W. Main). I was getting four tickets to My Fair Lady in the first balcony and they were coming out to about $400-450 online. Went to the box office and it was about $200 (not exaggerating). If you look closely on the ticketing website, there's a small disclaimer that says they are a 3rd party seller and prices may not reflect the actual ticket price. Such a scam.

I think the box office is open around lunchtime most weekdays - you could call in advance to check.