I was looking to upgrade my oxygenation setup from the disposable red bottles, and it took me way too long to find the perfect setup. I am posting this thread to help other homebrewers avoid this pain when upgrading their oxygen setup. The biggest issue was finding an inexpensive flow meter that connected to a welding oxygen cylinder. This flow regulator works great and is less than $30. You can control the flowrate from 1/2 liters/min to 8 liters per min.
The brass coupler was another difficulty to find. The regulator has a 9/16"-18 RH Thread on it called a DISS fitting (for oxygen).
You can purchase 20 cubic foot oxygen cylinders, but the local Airgas had 40 cubic foot ones on sale for $109. Once you purchase the cylinder, the gas cost about the same regardless of if its a 20 CF or 40 CF. With this size, I presume I am nano (or even micro) brewing ready if I ever decide to go pro. I'd recommend buying your tank local (you have to go there to fill it up anyways), but I gave a link online.
Here is the shopping list of supplies to buy your plug and play O2 system: