Well, hook knives pretty much suck vs heavier armors; on the other hand they are fast and very aimable. I suspect it would be of most interest to a rogue or ranger who uses brawling weapons and ambushes as a combat style. The value? Probably similar to a 6x dagger with that sort of crit weighting.
As to a specific amount, I haven't really a clue. I do have a brawling rogue who ambushes, although she prefers sais for that. I'll toss out an offer of a million as a baseline starter. Basically, the value is whatever folks are willing to pay for it, so let's see where it goes from there.
