There is a green CO2 regulator on ebay from China. It is about $40-45 shipped. I use this and it has been great. No leaks, steady flow, brass fittings, easy to adjust.
Most of the commercial regulators are made in China anyway...
Get one with the voltage of your country (110v)...
They all ship with DIN477 (european Co2 threads) but this doesnt matter because you will be converting to paintball tank.
You can get a DIN477 to paintball adapter from CO2Art in the UK. Its about $20. They also have good prices on the clear co2 tubing. They also have drop checkers, even though you dont really need one. You can add those to your order to get free shipping.
Buy a 24 oz paintball tank on Amazon. They are $23.
Get the tank filled at Dick's Sporting Goods for $5.
You need an API KH test kit and should already have a pH test kit. The KH and pH will tell you how much CO2 is in your tank.
Full paintball tank lasts on my 50g 7+ weeks.
Get one of those anti leak valves $5 from somewhere to keep water from siphoning into your Co2 regulator when it is off.
Keep Co2 tank vertical. You wont be able to use the bubble counter that comes with it. If you need to know your flow rate, disconnect the tube and put it in a clear bottle of water. Count bubbles.
Thats all you need. GL.