Quick answer: Milan runs about EUR 140 per day mid-range - noticeably less if you eat local and walk. Cheapest window: April-June and September-October - mild and lively; many local spots close in mid-August when the city empties.
What things actually cost
espresso at the bar
1.30 EUR
metro single
2.20 EUR
panzerotto at Luini
3.50 EUR
aperitivo with snacks
12 EUR
Duomo rooftop by stairs
16 EUR
Malpensa Express
13 EUR
Eat well for little
Risotto alla milanese (saffron risotto) at a classic trattoria - about 15 EUR
Cotoletta alla milanese - about 20 EUR at a traditional spot
Panzerotto at Luini behind the Duomo - about 3.50 EUR, the city's favorite snack queue
Aperitivo on the Navigli - 10-14 EUR for a drink with generous snacks, effectively a light dinner
Cappuccino and brioche at a historic pasticceria like Marchesi - about 6 EUR at the counter
Money mistakes to avoid
Not booking the Last Supper in advance - tickets are released months ahead in batches and sell out fast
Accepting free bracelets or corn for the pigeons outside the Duomo - it is a scam that ends in aggressive demands for money
Taking a taxi from Malpensa (fixed fare around 100 EUR) - the Malpensa Express train does it for 13 EUR
Judging Milan by the Duomo square alone - the city's charm lives in Brera, the Navigli and its aperitivo hour
Transport without the tourist tax
The Malpensa Express train runs to Cadorna or Centrale in about 50 minutes for 13 EUR (from Linate, metro line 4 goes straight to the center for a standard ticket). In town the metro is fast and clean - a single ride costs 2.20 EUR and the center is walkable between stops.