Vanya silk is not hard to get, you only need Potash x9 for the craft.

Potash can be obtained by trading in Tomestones of Philosophy @ Revenant's Toll, afaik 1 Potash costs 125 tomes.
And it's pricy because you need Vanya Silk for crafting the iLvl 70 Vanya Set of Healing/Casting which is atm the best crafted Healer/Caster gear in game.
And also, you'll need 1125 tomes for 1 Vanya silk, which translates into 12 Castrum or Pratorium runs (or 15 x Amdapor Keep)