Check out some info at www.mearstransportation.com and www.yourride.net If there are more than three people, it's cheaper to get a towncar from yourride or one of the other services. For one person, Mears Shuttle charges $14 per person from the airport to Universal.
You might also check out some of the discussions on the Transportation board. There are several town car services, one is a sponsor of these boards (FL TOURS). I think the most expensive would be a cab. Cheapest would depend on the number of people in your party.
Since the Hard Rock Hotel is an easy walk to City Walk (yes Cmatt, Margaritaville is here) you can take a shuttle to HRH and stroll over to CIty Walk. I'm not sure what you would do with your luggage, however.....