First, for long distance shots using a "portable" non-.50BMG rifle, forget about "production" rifles. You're gonna want a custom. That'll probably run you about $2,500 or so.
Add about a $1000 (or so) for a scope.
Add another $1,000 (or so) for precision reloading equipment. Things like neck turning tools, inside micrometers, etc.
Take your time to learn to use the stuff.
I'd recommend Bill Shehane (
www.scopeusout.com) and his 6.5/284 Shehane wildcat at 1,000 yards... Bill's one of the "kings" of thousand yard competition gunsmiths.
At further, you might be best served to give McMillan a call.