Traveling on a student budget makes you appreciate finding a good deal even if it takes a little bit of work; going to the opera is an amazing experience but going cheaply is even better! If you go to the Vienna opera house 80min before the start of the performance you can get a standing room ticket for only 4€ !! (I suggest the 4€ over 3€, better spot). Once you claim a spot at the cushy-bar (bring an item to claim it with, like a scarf), you are free to leave. Go grab a bite to eat in the area, you'll have plenty of time to spare! Additionally, don't worry about understanding the opera, there are numerous translators attached to the bars so you can read along in English.