Vienna, Austria + Add a trip

For the best place for lunch on a budget I would recommend "Der Wiener Deewan" http://www.deewan.at/ , which serves mild north Indian food for free, that is: financial contributions are voluntary.

The restaurant Liman has awesome Turkish food - great portions and low prices. They are open from 9:30 till 4 a.m. and offer great breakfast besides the usual main dishes. And if you order take-out or delivery, you'll also get insane amounts of fresh bread for free.

Der Tunnel, an old "Beisl", popular with students, live music evenings. The breakfast is legendary and only 3 EUR; but all other meals are very inexpensive, too.

Florianigasse 39

or you go to "li´s cooking" at the naschmarkt in the 5th district. nice asian stuff, and in case it´s full you have plenty of other restaurants around you :)