Free: Contests & Raffles.
I have looked at these links others provided and see that they are very affordable and easy.
Preassembled! WTH! Come on guys, everything you need to assemble is just a quick search away on Youtube. Seriously, it's pretty simple...
I have only got my hands on one or two i think they were called plumcrazy or something stupid like that but i was not impressed but i am sure there are some better quality ones out their.
If you are satisfied with a glock, no reason why you would not be satisfied with a poly ar lower. If you don't like the look and feel of a glock then I'd steer clear I have built a couple and no complaints. Sometimes I have had to do a little sanding in the tight spots but nothing major.working on a 300 blackout with one. Trying to get the whole thing under 5 lbs. I am at 3.25 lbls right now, just waiting for the bcg and carbon fiber barrel. Put a leupold delta point on it. Man those things are lightweight! I love it!