There is no way in hell you can buy off the shelf match ammo of any centerfire cartridge that meets your requirements for less than .25 cents. You can reload as big al hunter said.
With cost considered, I'd recommend the .308. There is a wealth of off the shelf match ammo and reloading components for it. With the .308 you can target shoot out to a mile. Also, it'll really test and improve your skills. It's fun because it's challenging. With both the OBR and P308 i can hit a 16 inch steel plate at a mile every time.
For a complete gun, I'd recommend either a pof-usa p308, or a larue obr. I personally prefer a p308. For long range make sure that you hand pick your gun, checking for any imperfections.
If you would like to build a gun, just get high quality parts that fit what you would need.