Are you running Nano tanks? Otherwise the cost of repeatedly refilling those paintball cylinders will cost a whole lot more than getting a real regulator. Also, paintball regulators are not known for their reliability. I have one 15# tank, with a splitter and two needle valves and I can run my CO2 24/7 on both tanks for 10 months. If they still have the one they listed on Craigslist maybe they will take a lower offer?
75 Gallon, 2X55W AH Supply CF 8800K, 1XMarineland Doublebright, 2X Marineland 350 Magnum; 45 Gallon Tall, 96Watt AH Supply CF 6700K; 30 Gallon Long; Fluval F&P 2.0 36"/46W; 20 Gallon, 1X26W AH Supply LED kit; all with Press. CO2; (Calcined) Montmorillonite Clay
Greater Seattle Aquarium Society (GSAS)