rubber city arms makes an adjustable gas key, this will likely be the cheapest option for an adjustable gas system, but not as easy to adjust as a gas block.
I have the superlative arms gas bleed block on my lightweight gun. Running an aluminum carrier and 1oz buffer. The click adjust is very nice, and easy, but the cost of that convenience is high (relatively speaking).
I have a spare lightweight steel bcg and am building a 7.5" lightweight pistol with poly upper and lower. I plan to put the adj gas key on that carrier and see how easy it is to adjust. Just takes more time between test shots to remove the carrier and tweak the screws.
I might get a cheaper "restictor" style gas block and try that out. I bought the rubber city keys to put on my 2 armalite ar10s in 308. one is very over-gassed, and the other may be under gassed. Delta team tactical has a adj block for 30 bucks, might have to give that a try.
Having an adjustable gas system really is the way to go. That way you can run the lightest buffer, and bcg and tune for the best recoil impulse.