Yeah, it looks like you're getting into the price range of a pressurized CO2 system. It's a novel setup, kinda neat, but for the price you may as well save a little more money and invest in a good pressurized system.
I just picked up a used 15# bottle for $50(the first one I've ever had to pay for), a regulator(new) for $52 including shipping, and 2 needle valves for $6 a piece. IMO, that's all you need for a decent pressurized system. The only additional expense is a $9 fill-up about every 4 - 5 months.
They are Clippard MNV - 2. I got them at a local distributor. Actually they were a bit less than $6. Around $5.75.
They are not knob adjusted, but rather screw-in adjustments. I feel I can make finer adjustments with the screw in's.
I am very happy with them and would recommend them to anyone.
I to have the clippard valve. I purchased mine at Air Engineering & Supply Co. 2719 East Franklin Minneapolis MN 55406 612-332-4181. Djlen is correct, these valves are awesome. I wish I would have known about them before I purchased a few others that were recomended. I paid less than $6 also for mine. I believe they are the only distributer in the tri state area so depending where you live it may be more.