Me, and many others here, chose to build rather than buy. Benefits include the ability to hand choose the parts you want rather than settling for what they give you. You also get an education in the workings of the platform, better to help you keep it running. Last but not least is the satisfaction that comes with the first rounds fired from the rifle that you built.
Cost will be just about the same as buying, biggest difference is that you will not have to upgrade the stock parts that come from the builder of an off-the-shelf gun. The AR platform is like an erector set for bigger boys, almost every part can be upgraded, modified or customized and there are hundreds of aftermarket brands and parts available.
"The whole of the Bill (of Rights) is a declaration of the right of the people at large or considered as individuals.... It establishes some rights of the individual as unalienable and which consequently, no majority has a right to deprive them of." (Albert Gallatin of the New York Historical Society, October 7, 1789)
"A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government." - George Washington