For a 12:01 flight you need to be at MIA not later than about 1030, and 10:00 or earlier is better with the typical TSA chaos (without pre-check the lines sometime take 45+ minutes to clear security! 😲). The ride from PE to MIA takes about an hour, which translates into off the ship, with bags and clear of customs/immigration NLT about 8:45 - again earlier is better!
A taxi from PE to MIA will run $75+ on the meter, so a total fare of close to $100 is a good ballpark. UberX or Lyft should be cheaper, but surge pricing may push those fares above what the cab will charge. The advantage with a taxi is not waiting - take the first one in line and insist that he use the meter. If you want to use a car/limo service, check with Larry's Limos who are often suggested on this board.
If any of this helps you owe me a pint - whatever bitter your local pours will be fine! 😎