easy to get a cab at the airport. Cabs from airport have a flat $52.00 fee (+ tip) to most of No. Miami Beach. But you must pick up at the cab rank outside arrivals/baggage claim. It will be about $60 + tip back. Call them they ll pick you up. Nobody refuses a fare to the airport. If you are traveling alone, Supershuttle is $27.00 per person. Pick them up outside arrivals/baggage claim; look for the blue yellow overhead Supershuttle sign. Slower, but half the cab fare. They ll even take you back, but you ll have to reserve at least a day ahead.
depends where in nmb, if it is the nicer part then you should be okay just know they will take a very long time. some part of nmb they will not show up at all. in south beach i have never had a problem but outside of sobe it can be challenging just call them way in advance