I bought a Kenmac KPR regulator for pressures up to 17barg with a Cv of 0.5 in brass (not stainless steel) for £212. Kenmac have been taken over by Swagelock, but still offer the same valves. I dont know the current price of this valve. My valve worked well. It gave high flow when required, held the outlet pressure well, and did not ice up with solid CO2 inside. It was fairly expensive!

Jeremy