I think patience, research and Ebay will give you the best result over time. I've had a RedSea paintball regulator, a Total Beverages regulator that I ran on paintball tanks with an adapter and I've even run Victor VTS 250 Dual Stage Regulators on Paintball tanks until I had a larger stand allowing a 5 lb cylinder. All of the setups did work, I never killed any fish but, you see the progression, I've spent money all along the way and ultimately, had to do the research and build my own. I've been using VTS 250s for about three years now and never had CO2 this easy. Dual Stage are truly...set it and forget it until the tank runs out. I just make sure it won't run out on the weekend though. :-)
Below is my first dual stage:
I bought 2 VTS 250s for $55.00 not including shipping. It was an Ebay auction.
The reason I bought VTS 250s is, if you see a VTS 253, meaning its' specifically for CO2, the price jumps. A CO2 specific nipple can be purchased for $10.00 in brass. a VTS 250 is for inert gas and works fine for CO2 if you swap the nipple and it saved me alot of money. Just took a little more research and questions from people here.