We use at CERN ALGADE RADHOME HRE and the indicative price is 12 k€ without certified calibration (+2 k€ and long delivery time). Otherwise), generic calibration coefficients for radon and thoron valid for the PIPS detectors can be used. If discrimination between Rn-222 and Rn-220 is of importance, a metallic grid allows to sharpen the peaks at a price of lower efficiency.
Hope U got very GOOD INFORMATION. I can only say that we were the First to use Radon Detectors in India; ALGADE, AlphaGuard, Plastic Detectors: LR-115 type 2 & CR-39, Smart Radon & Thoron Monitors in our laboratory. I am now retired but my friend, N. Katunakara has offered U help; Accept it.