Spirit Visage requires an additional Kindlegem, altogether costs 2750g Banshee's Veil doesn't need a Kindlegem, only the remaining Spirit Visage item builds, still costs 2750g.
Someone explain this shiet pls?
Just because the items it builds out of are less expensive doesn't mean the total value of the item's effects aren't worth equal or additional cost. That's about all I have to say
Spirit visage 
loses the unique passive of spectre's cowl 
, while banshee's veil retains it.
So spirit visage is cheaper
I think that's why, could be wrong
