It’s not cheap to stay in Miami [1], but visiting doesn’t necessarily have to be a budget-buster. During the high season (Dec.–Mar.) it’s possible to snag a decent room on South Beach [2] for under $200, with the rates decreasing the further north you go; during the summer, those rates can sometimes be reduced by as much as half.
To get the most out of a visit to Miami, staying on Miami Beach [3] is definitely recommended, since the concentration of restaurants and nightlife is at its highest, and you will only be a few minutes’ drive from the sights of mainland Miami. Those who choose to stay downtown tend to be business travelers.
Links:
[1] http://www.moon.com/destinations/florida/miami
[2] http://www.moon.com/destinations/florida/miami/accommodations/south-beach
[3] http://www.moon.com/destinations/florida/miami/accommodations/miami-beach