Uber from a hotel to POM should cost about $10 -the exact fare will be quoted to you when you book the ride, and you will see options for various types of vehicles (UberX, UberXL, Uber Comfort, etc.) at different prices.
Surge pricing indicates that there are a large number of requests for rides in an area with not enough drivers - passengers will need to agree to pay more and the higher fares should attract more drivers, eventually bringing prices back to normal. Surge pricing could push the fare up by a factor of 2, 3 or even 4 times the normal fare - the amount you will be charged will be displayed when you book your ride - if the fare is too high just take a taxi (meter fare from POM to MIA will be about $30+).
I would also set up a Lyft account - I always pull up both to see which has the cheaper fare and shortest wait for a car.
Have a great cruise!