I wasn't implying low cost is low quality. I was saying more cost gets you better parts most of the time. Good quality light weight free-floating hand guards typically cost more than their low cost counterparts like the ones used on PSA uppers for instance. They work good and are reliable but they weigh a lot more and the finish is basic. A good muzzle device and trigger are also going to cost you more that basic mill spec. One muzzle device alone on an AR-9 build I have is $180.00. Better is sometimes also referred to as better looking for those buying for the appeal. And when it comes to that beauty is in the eyes of the beholder.
9mm carbines can be a tricky build for some people also in terms of finding the right parts to have it work reliably with the right barrel, bolt, and buffer combo.