.223 Wylde with a good load and a good barrel is certainly 1/2MOA capable to 500 yards.

With the prices in the basement, I would bet you can build a complete upper for no more than $1200 that will give you everything you want and be at least $500 less than a factory built rifle. My Kreiger shot under 1/3MOA out to 600 yards and I built that upper complete for what would have been about $1k retail. If you need help putting one together, let me know.