Quick answer: Vienna runs about EUR 110 per day mid-range - noticeably less if you eat local and walk. Cheapest window: April-June and September-October for mild sightseeing weather - or late November-December for the Christmas markets.
What things actually cost
melange (Viennese coffee)
4.50 EUR
Wiener Schnitzel with potato salad
18 EUR
U-Bahn single ticket
2.40 EUR
sausage stand kaesekrainer
5 EUR
Schoenbrunn Imperial Tour
24 EUR
glass of gruener veltliner at a heuriger
4 EUR
Eat well for little
Wiener Schnitzel at Figlmueller or a neighborhood gasthaus - 18-20 EUR, traditionally veal, cheaper with pork
Sachertorte with a melange coffee at a classic cafe - about 12 EUR for both
Kaesekrainer sausage from a wuerstelstand - the late-night classic, about 5 EUR
Naschmarkt stalls - mixed mezze plates and market snacks, 8-12 EUR for lunch
Apfelstrudel with vanilla sauce - about 6 EUR at a traditional cafe
Money mistakes to avoid
Not planning around Sunday closures - most shops and many restaurants close, so save museums and cafes for Sunday
Buying concert tickets from costumed Mozart sellers on the street - book reputable venues like the Musikverein directly online
Only staying inside the Ringstrasse - the 4th and 7th districts have better food at lower prices ten minutes away
Forgetting to validate your metro ticket in the blue stamping machines before boarding - fines are around 100 EUR
Transport without the tourist tax
From the airport, the S7 train reaches the center in about 25 minutes for around 4.40 EUR (the faster CAT costs 14.90 EUR). The U-Bahn and trams cover everything; a single ride is 2.40 EUR and a 24-hour pass about 8 EUR.