That seems to be the cheapest I have found so we will probably go with it
You may also want to look into taking a taxi, depending on how many people in your party. I think it's about $75 each way, including tip, to taxi from Miami Airport to Port Everglades. If there are two of you, Royal Caribbean's transfers are a good deal. With more than two, it may pay to take a taxi.
On the way home, make sure your flight is later than 12:30pm. If the ship is delayed in getting cleared, you may be getting off the ship later than anticipated. Also, if you're among the first to get on the transfer bus, it won't leave until the bus is full, which could take 30+ minutes. It's true that if all works quickly, you could end up at the airport early, but it's better to take the stress out of that last morning and book an afternoon flight home.