A miniature neon indicator lamp, also known as a Glow Discharge Detector (GDD), costing about 50 cents, was found to be an excellent room temperature THz radiation detector. A proof of concept of 300 GHz heterodyne detection using GDD is demonstrated in this paper. Furthermore, a comparison to direct detection was carried-out and polarization effects on heterodyne detection were investigated. Preliminary results at 300 GHz showed better sensitivity by a factor of 20 with only 56 microwatt local oscillator power using heterodyne compared to direct detection. Further improvement of the detection sensitivity can be achieved if the Local Oscillator (LO) power (Plo) is increased. Effects of orthogonal polarizations of signal and local oscillator powers on heterodyne sensitivity were found to be surprisingly weak. More efficient quasi optical design for heterodyne detection is presented in this study, experimental results showed above 50% better performance compared to conventional ones.