Quick answer: Mexico City runs about EUR 60 per day mid-range - noticeably less if you eat local and walk. Cheapest window: March–May.
What things actually cost
taco al pastor
0.90 EUR
metro ride
0.30 EUR
fresh juice from a market stall
1.50 EUR
Uber 20 minutes
4-5 EUR
craft beer in Roma Norte
3.50 EUR
Frida Kahlo museum entry
about 14 EUR
Eat well for little
Tacos al pastor carved off the trompo at El Vilsito or El Huequito - about 0.80-1 EUR per taco, go after 8pm
Tostadas de atun at Contramar - the famous split-sauce fish and tuna tostadas, expect 25-35 EUR per person and book ahead
Churros with hot chocolate at El Moro - open since 1935, a plate runs about 4 EUR
Tostadas Coyoacan inside Mercado de Coyoacan - heaping seafood and tinga tostadas for 2-3 EUR each
Tlacoyos and quesadillas from blue-corn street griddles - 1-1.50 EUR, pick the stand with a line of locals
Money mistakes to avoid
Ignoring the altitude - the city sits at 2,240 meters, so take day one slow and drink more water than usual, especially with mezcal
Hailing taxis on the street - use Uber or DiDi instead, they are cheap and the safe standard here
Choosing empty street stands - busy stalls with high turnover are both the tastiest and the safest bet for your stomach
Leaving Teotihuacan for midday - the pyramids have zero shade, so arrive when gates open at 9am and be done by noon
Transport without the tourist tax
From the airport an authorized taxi or Uber to Roma or Condesa takes 30-45 minutes and costs 8-12 EUR depending on traffic. In town the Metro is a flat 0.30 EUR a ride, and Ubers between neighborhoods run 3-5 EUR; avoid the Metro at rush hour with luggage.