There is no XP cost if I have Grindstone Disenchanting enabled.
Is it possible to set XP Cost in the Config? I can not find it!

grindstone disenchanting has no config to add xp cost.
iirc the mechanics downside is that it forces all the enchants to be transfered at once.
adding a xp cost would be a new feature and atm we're are not adding feature requests.