Marty,
It all depends on supply and demand on these items. I catch about 2 a month at the local junkyards (whenever an Aspen stationwagon dies).
I usually can pick up the whole stack (pie tin,carb,both manifolds,kickdown linkage,vacuum tree & Amplifier) for $30 if carb is hot and exhaust manifold is cracked, to about $50-60 if the car still ran when they junked it. You might look around some more, or check with some other members and see if they have a spare they might part with. I had two spares, but they are already spoken for.
I understand also that pre-72 BBD, and the super six BBD had no holes in the throttle plates and make good substitutes. I have actually gotten away with soldering the holes shut in a 318 BBD but did worry about a backfire destroying my 5 minute "patch".
good luck,
-DusterIdiot
res0aus2@verizon.net