Quick answer: Miami runs about EUR 190 per day mid-range - noticeably less if you eat local and walk. Cheapest window: December-April - dry, sunny and warm; June-November is hot, humid and stormy with hurricane season peaking August-October.
What things actually cost
cafecito at a ventanita
2 EUR
Cuban sandwich
10 EUR
beach chair and umbrella rental
18 EUR
rideshare South Beach to Wynwood
15 EUR
cocktail at a beach bar
14 EUR
mid-range hotel double per night
170 EUR
Eat well for little
Cuban sandwich at Sanguich de Miami or Versailles - about 10 EUR
Cafecito and a croqueta from a Little Havana ventanita window - about 3 EUR
Stone crab claws at Joe's Stone Crab (season runs October-May) - the classic splurge, about 40 EUR and up
Ceviche in Wynwood or Brickell - about 15 EUR
Empanadas from a Latin bakery - about 2.50 EUR each
Money mistakes to avoid
Renting a car for a South Beach-only stay - parking is scarce and 25-40 EUR a night; walk, trolley and rideshare instead
Sitting down on Ocean Drive without reading the menu - check for automatic 18-20 percent gratuity and inflated drink prices
Underestimating the summer - plan mornings outdoors and expect a drenching afternoon thunderstorm June-September
Ignoring the colored beach flags - rip currents are real; red flag means stay out of the water
Transport without the tourist tax
From MIA airport the Metrorail Orange Line reaches downtown for about 2 EUR, while a rideshare to South Beach runs 25-30 EUR. On the beach use the free trolleys and Citi Bike; between the beach and mainland neighborhoods you will rely on rideshares at 12-20 EUR a hop.