past week I've seen:

VH ASI Sealed swords go for 15k CE
VH ASI Divine Avengers go for 17-20k CE
VH ASI Gran Fausts I haven't seen in a while, but they're made from the same stock as the Avenger line, so see sealed sword above. I guess in the end it comes down to whether or not someone was planning to make a GF in the first place.

I love the GFaust. But I also love the Acheron. The Faust just took longer to grow on me. :D
(I got my faust [4 star] for 11.8k CE, just for reference, but that was long before lockdown came to town)

Personally I've seen them go for about 18-35k CE as well. And since the demand had died down I haven't seen the market flooded with sealed swords focusing on ASI anymore. Most of the people rolling have been going for CTR on DA's so this is actually a very moderate price in my personal opinion given the fact that it's already been crafted to 5* gear. You pay for convenience as they say.

As for the usefulness of a GranFaust ASI VH is you can wear 1 piece of Vog and 1 piece of Skolver for a mixed defense bonus and still have max ASI and at least a medium sword damage bonus. With a barb shield and even one Damage trinket you can sit at Max ASI/Damage. For a GranFaust ASI is key for DPS as using a charge attack on a GF is kind of silly given the chance for cursing oneself(Not a huge issue if you have 4 weapon slots, but still a pain if you've locked your optimal weaponry due to GF charge spam). It's pretty darned good since the damage bonus transfers well if you use a Med-VH CTR DA too, as the ASI bonus to the DA isn't as important for DA Charge attack spams and the % to total damage from skolver/barb shield/trinket means being able to clear arenas with a more effective increase to DPS than the ASI from Vog would support. So I guess what I'm saying is a sword like this would allow you to maximize your damage output a bit more efficiently than you would normally have thought. Especially for a loadout that would operate as a catchall for most depths of the clockworks.

But all of that is just from a Crafter/Seller that likes to try to be as efficient as possible in terms of damage and proper defense coverage.

/rant