Quick answer: Lisbon runs about EUR 90 per day mid-range - noticeably less if you eat local and walk. Cheapest window: May–June or September–October (warm, fewer crowds).
What things actually cost
espresso (bica)
0.90 EUR
pastel de nata
1.40 EUR
metro ride
1.80 EUR
glass of vinho verde
3.50 EUR
bifana sandwich
3.50 EUR
lunch menu at a tasca
10 EUR
Eat well for little
Pastel de nata at Manteigaria - warm custard tarts for about 1.40 EUR, better queue than the famous Belem shop
Bifana - garlicky pork sandwich at O Trevo or any tasca, around 3.50 EUR with a beer for 1.50 EUR more
Grilled sardines in Alfama - a plate with salad and potatoes runs 10-12 EUR, best in summer
Seafood at Cervejaria Ramiro - garlic prawns and crab, expect 25-35 EUR per person, arrive before 7pm
Ginjinha - sour cherry liqueur from the hole-in-the-wall bars near Rossio, 1.50 EUR a shot
Money mistakes to avoid
Riding tram 28 at midday - hour-long queues and pickpockets, take it before 9am or just walk the same route
Eating on Rua Augusta or next to a miradouro - walk two streets away and prices drop by a third
Not knowing the couvert rule - the bread, olives and cheese brought to your table are charged, send them back if unwanted
Packing only smooth-soled shoes - the polished cobblestones are genuinely slippery, especially when wet
Transport without the tourist tax
The metro runs from the airport to the center in about 25 minutes for 1.80 EUR, or an Uber costs 12-15 EUR. In town walk plus metro and trams with a rechargeable Viva Viagem card - a 24-hour transit pass is about 6.80 EUR.