There are currently major roadworks and tailbacks around San Pedro de Macoris. They might still be there around December, so the drive from Santo Domingo airport to La Romana can take 2 to 2.5 hours instead of 90 minutes. If the motorway has been completed then I guess the drive will take just over 60 minutes.
Taxi is the easiest way to travel (prices quoted in post #1). Public transport is a pain, especially if you don't speak Spanish and have luggage.
Hotel Vecchia Caserma is reasonably priced for an overnight stay and less than a 10 minute drive east of La Romana Port. It's inland so no beach access. Taxi will cost around $US30 to the port.
hotelvecchiacaserma.com/index.php?lang=en The motorway exit is marked Boca de Chavon/La Flor Cigar factory.
Edited: 12:42 pm, August 31, 2013