If this item is NOT reproduced as you say (I have never looked for them), price is as you suggested based upon supply vs. demand. coupled with the willingness of the buyer's patience and budget.
This would be the same basic guide for ANYTHING limited in availability. Many, if not all of the items you have been seeking are not often sitting around collecting dust here in the states. If it is, it is lost in somebody's garage and we, who know what they might be worth, have no knowledge of them or need them ourselves.
My opinion, these moldings you were seeking could have been less if you could wait several months, having somebody here in the states scouting for them...Other times, simply buying what you find is the best deal possible AT ANY PRICE. Peace of mind is worth much more than a few hundred buck (or Euros)