sorry, but that is TOO low
you are looking more at a scabbard of keen edges instead of a quiver of ehlonna, which essentially makes any weapon placed in it, a keen weapon (which is a +1 enhancement). this is more appropriate than your interpretation.
The scabbard runs at 15000 gold. to add the quiver ability is pretty mundane, and I would just add the prices together to get 16800.
Scabbard of Keen Edges
This scabbard is fashioned from cured leather and fine silver. It can shrink or enlarge to accommodate any knife, dagger, sword, or similar weapon up to and including a greatsword. Up to three times per day on command, the scabbard casts keen edge on any blade placed within it.
I'd also rule that the quiver would only affect 60 arrows at a time, since that is the capacity of the quiver of ehlonna, and could only enchant them three times per day with the same duration as the spell "Keen Edge". That's being generous in most cases, as most spells only affect 50 arrows, so there probably would be a 20% addition for the extra 10 arrows.
the problem in your logic is that you are adding unlike bonuses together as a single bonus. The problem is that the general makeup of calculating item costs is that any additional "features" you add to an item generally have their cost doubled. (a third effect would in turn be tripled).
the other problem is that you were calculating how much it would be to make the quiver "seeking", not the arrows. You could in turn make the quiver seeking, but it wouldn't do much damage. In turn, if the quiver granted this ability to an infinite number of arrows, then you are circumventing the original price for the "seeking" enhancement, which costs 2000 gold for 50 arrows, not an unlimited supply.
I think the 16800 is a fair price for an item of this sort, but I would definitely limit the number of uses per day (3) and the maximum number of arrows that were affected per use (50).
Dursk.
