I think if you're going to do "base model" for plinking (shooting steel or reactive targets, etc.) inside 200 yards you may as well buy an off-the-shelf rifle. You won't really save any money buying components and rolling your own at that price point without really shopping the sales and bargain bins (and paying shipping on all that stuff). Or, buy someone else's regret, and let them take depreciation on post-Newtown madness since back to almost normalcy.
Then you can change it as you desire -- change the trigger, grip, buttstock, and maybe the hand guard to suit your shooting wants and needs.
I looked at all the options out there, did my research, and found that I wanted a highly accurate target/predator hunting rifle. Others may want something more "tacticool" with lots of rail space, back-up iron sites, lights, lasers, etc. Others just want the base model, or one that looks and feels like what they lumped through the deserts of Iraq or with a carry handle as in Viet Nam. Do you want a flat-top upper (A3) with an optic?
By building mine the way I wanted it in the first place, I didn't have any take-off parts. But my rifle isn't exactly a basic model (IMHO). I selected exactly what I wanted, and the *only* take-off part left over was the plastic handgrip (I used an Ergo instead) and the flat-bottom of the trigger guard (I got a 'winter' trigger guard).
I spent a little more up-front to get to my desired end result sooner, versus buying a base model and 'upgrading' it & ending up with a box of take-off parts.
If I'd have wanted the basic model, I would have just bought the M&P Sport, Delton, Windham, etc. and been done with it.
It all really boils down to what do you want to DO with it? Then you balance what is the expected level of quality, refinement, accuracy, weight, rail space, barrel material (chromed or not), barrel length, DGI vs piston-driven, whether or not you want it threaded for a brake, which adjustable buttstock, the COLOR, etc. all come into play.
It's a fun learning experience. I read a LOT on the Internet, bought AR buyer's guides at the Wal*Mart magazine rack, etc. before spending anything.