Ideal dream scenario is to find a crashed G body with a solid drivetrain. The little stuff, aside from being hard to find, can nickel and dime you to death. A shop usually just calls the parts house for it, not look around for the best deal on a hard to find part.
I would stay away from a "0 mile" anything. They're usually bare, and seldom 0 mile....lots of Krylon rebuilds out there. Better to buy a dirty one out of a fresh kill, barring finding a donor car.
Vortecs are good engines, but a manifold and carb to use it are going to eat up a lot of your budget. TBI engines also will require a manifold and carb to use.
Like I said, best bet is a donor car, preferably G body, as it will have all the stuff you'll need...mounts, fan shroud, maybe larger radiator, bracketry, etc.
I'll probably get flamed for this, but 4 doors make great donor cars, as there is usually little interest in them once they're no longer driver-status.