Transfers can be arranged from Sofia airport to Bansko which is advisable in the winter for skiing journey time is approx 21/2 hrs. But in the summer it is worth hiring a car to explore up into the mountains and visit the surrounding villages.
There is a bus service to Bansko from the Sofia bus terminal which takes approx 31/2 hours.
You can also fly to Plovdiv again transfers are available and car hire. Journey time approx 3hrs 15mins as there is no motorway.