Palmetto State Armory has some of the best deals going.
Their assembled uppers, using the FN barrels are some of the best available for the price. You can build/assemble almost any package you want right off the website and just pick up a lower locally and be a great deal ahead, no specialty tools needed either.
One tip, try and stick with one brand for major parts, some manufacturers tolerances are not friendly with each other.
And stick with the metal receivers for a hard use gun, I’ve seen three poly receivers fail under minor strain.
I bought a wmd carrier and bolt. All nickel boron plated and ready to replace my old bolt. It seems a bit heavier and more rugged than the old one. It came with the trigger but no spring. Now I’m wondering ifI should replace the spring. I’m going to oil it anyways or should I say Ballistol it. I finally managed to save enough spare change to buy a gallon.