I have spoken to the person who sold these and they came direct from the Schleich factory in Germany. Nobody knows how many (if any more) of these exist.

Generally though out of the "normal" smurfs the following in my opinion are probably the ones that fetch the highest price on a regular basis:

Praying smurf
Praying smurfette
Christmas wreath smurf
Baseball smurfette
Green suprise bag
Orange suprise bag

There are of course many variations and promos that will fetch far more than the normal smurfs (see interesting auction on the board for an example).
At the end of the day though it really is up to how much somebody is prepared to pay.