Get yourself a stripped lower and then contact either Del-Ton or Bravo Company for a parts kit. You’ll be able to put a decent AR15 together that way for about $500-$600. Then you can customize as you see fit.
If you have no experience assembling AR lowers, I’m sure there are competent smiths around you that can.
Of course I'm taking it with me on my white water rapids trip next month. ;)