Tank (20gal min.) and tank lid - Screen top is ok if you cover most of it with foil, plastic sheet, plexiglass, etc to keep heat and moisture in. An even better and more economical option is to use a clear plastic storage tub. You can increase the tub size as the snake grows. An adult BP can live its entire life in a 41qt tub. Drill holes in the sides of the tub near the top for ventilation. Tubs hold moisture great. The only drawback is that the room must be kept at about 78 degrees or so year round. A dome fixture and heat bulb can be used with a screen top if the room is too cool, but keep in mind that it will kill the humidity in the cage.
Under tank heater - Properly sized for your tank or tub
Thermostat - Hydrofarm is fine to start out with. http://www.amazon.com/Hydrofarm-MTPR...ords=hydrofarm
Digital Humidity Gauge/Thermometer - I got my Accurite gauge at Walmart for $8.94
Properly sized hides for both cool and warm sides
Water bowl
Substrate material - I prefer cypress mulch because it looks good and holds humidity well, but there are many other options out there. Avoid Pine, cedar, or fir as they are harmful to a reptile.
Infrared heat gun- You can find these at Petco or Petsmart pretty cheap. Home Depot and Lowes carry them as well.