Are more expensive AR's significantly more accurate?
Title says it all. I'm not sure what rifle I'm going to end up with (got a little while of saving up money first before I can choose). Lately I've been contemplating getting an AR so that I could have a 5.56 upper for short range competitions and then switch to another caliber for longer range shooting. I do have a bolt .308 so 1200 yard accuracy won't be the end goal. Just something that could be taken out farther a little more easily than the 5.56.
My question is, is there a significant difference in the accuracy between "mid level" and fancy AR-15's? Would an off the shelf S&W MP-15 be handicapped under a Stag Arms or Noveske? I understand there's probably a price difference but will a lower level significantly hold me back? And, if so, can they be upgraded to the same (ish) level of accuracy without essentially replacing the whole rifle?
In the interest of full disclosure, I would probably only be able to afford a mid level entry at first (if even an AR) and anything more expensive may have to wait as I have to start saving for many more important things as well.