So I decided it is time for an Ar. I can get at cost a Bushmaster M4A3 flat top complete upper for 389+tax. I am unsure if it is a heavy barrel or if it is chrome lined though. I picked up an ATI Teflon coated stripped lower tonight for $75 new. I want to keep it as close to an m4 as possible. I want a flip up rear sight but fixed front sight. I want to do some small stuff like a Magpul trigger guard and Magpul stock. I kinda want a quad rail but the fore grip on the upper is a short fore grip as opposed to a longer one so the quad rail may look goofy. My question is should I spend extra on a better upper or build one from scratch some where. I want to keep it at around a $700 budget since I can get a complete parts kit from bushmaster for $40, the upper for $389 and have a lower for $75. Also does anyone have a hookup somewhere or have a business that I can get some good deals through?