St. George Regional Airport: Rent a car at the airport; Virgin is roughly 45 minutes away via I-15 and UT-9. Expect about US$50–100 per day before fuel for a basic rental, varying sharply by season. There is no useful direct public-transport link to Virgin, and rideshare availability is too thin to plan around.
Harry Reid International Airport, Las Vegas: A rental car is the practical choice: about 2 hours 15 minutes to Virgin via I-15 and UT-9, assuming normal traffic. Las Vegas has many more flights and usually better car availability than St. George. Do not book a Las Vegas–St. George shuttle unless your Virgin lodging has arranged the final leg; getting from St. George to this small town is the problem.