Huatulco International Airport (HUX) is only a 15-20 minute drive from the resort areas, making for an easy experience coming and going. The facilities at the diminutive airport are modern and comfortable. Recent expansions in 2013 have nearly doubled the size of the airport from a few years ago, and it's become more pleasant than ever to use. The lack of flights to Huatulco from the US and Canada has been a sore point among local business owners. Things seem to be improving in the last few years with Aeromexico and Interjet offering budget service to Huatulco via Mexico City. Interjet is not linked into US and Canadian booking networks and tickets have to be bought directly from their website. At any given time there are various charter operations too, with Frontier operating direct flights out of Chicago one day a week from Jan 18, 2014 through the winter season, and Sun Country out of Minneapolis offering direct flights through the winter. Sunwing offers charter service out of Canadian cities.
United flies daily nonstops from Houston to Huatulco from Dec 18 - mid April. The rest of the year they pretty much only fly on Saturday, sometimes on Wednesday.
Interjet has a couple of flights a day from Mexico City to Huatulco on a regular jet as does AeroMexico Connect.
Rental cars are available at the airport from Thrifty, Advantage, Hertz, and Europcar. Make a reservation online and the prices can be shockingly cheap, as little as $130/week. The problem is they're not likely to respect the rate, or they will load on so much mandatory insurance that the price goes to $300-400 a week. A better option in Tangolunda is Oaxaca Rent-a-Car, which has set rates with everything included, usually cheaper than the airport rental places.
Just as it is at most airports of the world, taxi service from the airport is a racket - the taxi concession that has exclusive rights charges $45. (That's for the whole car. Don't let them try to charge you $45 per person.) There is colectivo service by taxi, where you share with other people, that only costs 120 pesos or so. Make sure you insist on a colectivo, they sell the tickets at the same place they sell the normal taxi fares, though I've had friends say they've been misinformed by airport staff at times that colectivos aren't possible from inside the airport. Taxi service to the airport is only around $12 from any cab in town. Once you're in town, taxi service is surprisingly cheap to get you on short trips around town. Anywhere in La Crucecita, and between La Crucecita and Santa Cruz or Chahue, is 25 pesos ($2). For more extended trips, the prices get a lot more expensive.

For those coming or going around Mexico by bus, the very modern bus station is on the north side of La Crucecita on the main road into town. Buses leave here for just about anywhere you can think of in southern Mexico.