GunThings.com, Military Small Arms Parts Headquarters! FNFAL, L1A1, 1919, AK, Galil still has them pre-barreled with extension, including new sling, Colt-stamped magazine, and cleaning kit; for $599.00.... imho, a better deal than APEX's parts kits. However, APEX sells the unissued sling, magazine, and cleaning kit, but no barrels or extensions. APEX's total comes to $420, with everything they have available...
If you can dress and park/paint/other finish your own barrel, you'd probably be better off getting all your stuff from APEX. If you'd like a kit that's ready to go, get it from Gunthings.
Just got mine ordered today from gunthings... Would rather someone with a bit more M16A1 experience barreled my next black rifle. :P