Combat for what is the question. If it is going to be a SPR type thing, there is one list, and if it is like a room to room clearing gun, a completly different list.
SPR:
Lower:
POF-USA P-415 GEN III Stripped Lower $325.00
Rock River Arms Ambidextrous Safety Selector $25
Rock River Arms Lower parts kit $70
Geissele Hi-Speed Service Rifle Trigger $280
Magpul PRS Buttstock $250 or Command Arms Accessories SRS Buttstock $400
Magpul MIAD Pistol Grip $45 or ERGO Tactical Pistol Grip $60.00
Buffer Technologies Enidine Hydraulic Recoil Buffer AR-15 $89.99
Upper:
Larue Billet Stealth Upper $250
PRI Gen III Free Float AR-15 Forearm System Rifle $328
PRI GAS BUSTER CHARGING HANDLE / BIG LATCH $90
Krieger Barrel $400
LMT 5.56, Enhanced S/A Bolt Carrier Group for .223/5.56 $285.00
Dynamic Armament Gas Block .936 AR-15 $30
Daniel Defense AR15 Aluminum Barrel Nut $40
Bushmaster Gas Tube $15
Bushmaster Delta Ring kit $14
Bushmaster Hand guard Weld Spring $5
Larue Tactical SPR / M4 Scope Mount QD LT-104 $200
HORUS HAWK 3-12x50 $500
Surefire FH556-212A Suppressor adapter $300?
Surefire FA556-212 Suppressor $1,200
For a short carbine; something like this:
http://noveskerifleworks.com/cgi-bin/imcart/display.cgi?item_id=r-lslp-556&cat=47&page=1&search=&since=&status=
Or this:
http://www.pof-usa.com/upper/upper415-6119X.htm
Sometime i will make a list like above for it.....
To either of these, a DIAS is NEEDED.