Bansko, the popular ski resort, is an important entry gate for the Pirin range.
In order to reach the Banderitsa or Vihren huts/chalets (base camp to hike in the area), at least in the non-ski season, you will either have to hire a taxi (~$15), go with a tour, or hitchhike.
The best option for independent traveler(s) on a budget is to hitchhike, which is particularly easy during the summer with a good amount of domestic tourists heading up to either of the camps. To do so, walk south (gently uphill) though town until you reach the entrance to the Pirin National Park, indicated by a small house for information about the park. From there, the only cars going will be into the park.
Once inside you will have to hike, the different huts and summits are connected by hiking trails. There are many different options for hikes, with indications on how many hours each hike will take at a moderate, comfortable pace. If you plan to spend a while hiking, check with the tourist office (during normal business hours) to get a map of the area and plan out your hike.
There is a broad network of flagged trails through the mountains. The Pirin tourist map (1:50,000, avalable at local shops) offers a good overview of the trails and huts/chalets to sleep in.
Most of the mountain huts offer cheap meals.
There is a network of mountain huts, which offer rooms and bungalows (bungalow for about 10 Dollars for two persons). Bring your sleeping bag. Alternatively there are marked camping areas around the huts.