I just completed my AR build and have about $1,250 into it. But, to be fair, I had a 20" Colt barrel and bolt carrier (no bolt), - all other parts had to be purchased.
I did pay for some premium parts which include:
Matched billet 7075 receiver set
7075 buffer tube
7075 one-piece free-float 12" rail system with end cap
Nickel Boron plated bolt (already had M16 Chrome bolt carrier)
Magpul ACS stock
Steel Miculek Charging handle
The thing is rock solid - no rattles, gaps or things that don't fit together smoothly. So, I am very pleased with my build - just need to find time to shoot it and see how it groups.
I went "cheap" on the iron sights for now - decided to go with some standard bolt-on front and rear sights - no flip sights. They are pretty rock solid and I think they will hold zero pretty well - we'll see.