Based upon price point vs quality, it is nearly impossible to beat the Colt 6920 (M4 Carbine). Here are my recommended Colt M4 Set Ups based upon three budget levels:

LOW BUDGET

Colt 6920 M4 Carbine = $825 +/-
LMT Fixed A2 Rear Sight = $80
PRI Big Latch (charging handle latch) = $25
SureFire G2X LED Light = $55
Viking Tactical Offset Light Mount = $24
MagPul Rail Section (to mount the VTAC to) = $5
2pt Sling = $25
(10) 30rd Magazines = $200
Total Weapon System Cost = $1,239


MID BUDGET

Colt 6920 M4 Carbine = $825 +/-
Troy Flip Up Rear Sight = $100
Aimpoint PRO Optic = $375
PRI Big Latch (charging handle latch) = $25
SureFire G2X LED Light = $55
Viking Tactical Offset Light Mount = $24
MagPul Rail Section (to mount the VTAC to) = $5
2pt Sling = $25
(10) 30rd Magazines = $200
Total Weapon System Cost = $1,634

HIGH BUDGET

Colt 6920 M4 Carbine = $825 +/-
Troy Flip Up Rear Sight = $100
Aimpoint T2 or M4S Optic with LRP Mount = $700
PRI Big Latch (charging handle latch) = $25
SureFire 600 Scout Light = $200
KAC RAS Rail System = $150 (these are getting cheaper)
2pt Sling = $25
LMT SOPMOD Gen2 Stock = $150
MagPul MIAD Grip = $30
(10) 30rd Magazines = $200
Total Weapon System Cost = $2,405

You can have a fully functional Tier-1 Fighting Rifle for as little as $1,239. This was the BASE COST of a Colt 6920 M4 Carbine a couple of years ago.