Quick answer: Munich runs about EUR 140 per day mid-range - noticeably less if you eat local and walk. Cheapest window: May-June and September - warm beer garden weather without peak Oktoberfest prices (late September brings the festival and triple hotel rates).
What things actually cost
espresso at a cafe
2.80 EUR
Mass (1L) of beer in a beer garden
9 EUR
Weisswurst breakfast
8 EUR
single inner-zone transit ticket
3.90 EUR
Residenz palace entry
10 EUR
mid-range dinner main
18-22 EUR
Eat well for little
Weisswurst breakfast with pretzel and sweet mustard - eaten before noon by tradition, about 8 EUR
Mass (1L) of Augustiner in a beer garden - about 9 EUR, half liter about 4.50 EUR
Schweinshaxe (pork knuckle) at a traditional Wirtshaus - about 18-20 EUR
Viktualienmarkt snacks - Leberkaese roll for about 4 EUR, cheese and fruit stalls for a picnic
Kaiserschmarrn for dessert - shredded pancake with plum compote, about 9 EUR
Money mistakes to avoid
Only drinking at the Hofbraeuhaus - it is fun once, but locals drink at Augustiner Braeustuben where beer is cheaper and food better
Forgetting shops close on Sunday - stock up on snacks and essentials Saturday
Underestimating Oktoberfest season (late Sep to early Oct) - hotels triple in price, book months out or avoid those weeks
Transport without the tourist tax
From Munich airport the S1 or S8 S-Bahn reaches the center in about 45 min, roughly 13-15 EUR (the airport-city day ticket is good value). The old town is walkable and the U-Bahn/tram network covers the rest - a single inner-zone ride is about 3.90 EUR.