It's 16 miles or 30 minutes in good traffic.

I'm fairly sure a taxi cab to Bal Harbour is fixed - but I don't know how much as I alway have them take me to South Beach. A cab ride to anywhere in South Beach is fixed at $28. I recall seeing a notice inside of a Miami cab that listed all fixed-priced fares and Bal Harbour was one of them - I just can't remember the price. The good news is that in Miami, the price of cabs does not depend upon the number of passangers or luggage. In fact, you can request a minivan from the nice cab man at the airport (who will not accept tips) for the same price. It may take a few extra minutes, but if you have say four travelers and lots of luggage, it's worth the wait.

A quick google search and I found www.miamitaxi.net/transp/taxi_tips.htm. According to this web site (and it appears to be current), a cab ride from/to MIA and Bal Harbour is fixed at $38. My guess is if you have two or more passangers, this will be cheaper than a shared bus service and a lot quicker. I never get a rental car unless a cab ride is REALLY expensive or I need one for long distance trips such as to a business customer. I hope this helps.