I wanted a K.I.S.S. carbine but I wanted something nicer than some of the "plinker" guns on the market. I wasn't brave enough to go for a full build so I searched the equipment exchange pages here and at AR15.com and found what I was looking for.
I bought a complete DPMS 16" upper with 5.56 NATO chamber, 1:7 twist, chrome-lined chamber and bore with A-1 sights, A-2 flash hider and bayonet lug. I bought an Olympic lower with A-2 butt stock from another guy and just pinned them together.
I'm very happy with the outcome and I've got a grand total of $605 invested in it, including shipping and FFL transfer fee for the lower.
To a much greater extent than most mechanical devices, firearms are terribly unforgiving of any overconfidence, complacency or negligence.