I have unlocked 11 items in 9 traits and will have 15 next tuesday. I was thinking of around 30k for 5 pieces (full set). Maybe that's a bit low, I'll adjust depending on demand.
The Way of the Arena set was worth 10k/piece at the very beginning and it was much easier to access than Twice-Born Star.
After patch 1.5 nirncrux will be a lot cheaper. On my server it is going for 10k-15k still but after playing on PST and getting 5 nirncrux from one advance node (after finishing the new crafting quests) So I expect nirncrux to drop to around 5k each.
Still 9 trait sets will be rare (not that many crafters have finished the research, so I would expect 2k to 10k per slot (excluding nirncrux costs if they want that trait)