This paper is concerned with the design, development, and autonomous flight testing of the GT Lama indoor Unmanned Aerial System (UAS). The GT Lama is a fully autonomous rotorcraft UAS capable of indoor area exploration. It weighs around 1.3 lbs (600 gms), has a width of about 27.6 inches (70 cm), and costs less than USD 900. The GT Lama employs only five off-the-shelf, extremely low-cost range sensors for navigation. The GT Lama does not rely on other expensive and sophisticated sensors, including inertial measurement units, Laser based range scanners, and GPS. The GT Lama achieves this by using simple wall following logic to ensure that maximum perimeter of an indoor environment is explored in a reasonable amount of time. The GT Lama hardware, and the Guidance, Navigation, and Control (GNC) algorithms used are discussed in detail. The details of a MATLAB based method that facilitates rapid in flight validation of GNC algorithms on real flight hardware is also discussed. Results from flight tests as the GT Lama autonomously explores indoor environments are presented.