I guess that all depends on size, materials, time it would take to make.
If you wanted say a Kermit size puppet, that could cost roughly $150-$200 dollars. But a puppet like Gonzo, with the amount of sculpting involved, could be much more. The cost could be less ($20 or so) if the puppet you wanted was more of a "toy size," like the old FisherPrice Muppet puppets from the 70's.
That's just my thought on the matter. Hope it helps!
patrick