Nah, it makes sense, since I think Bioware based the "cost" on the assumption of 100 (or rather 99) arrows in a stack, not 500. I don't think we refigured the cost profile when we changed the maximum stack size, and since it doesn't seem to affect play negatively, then it's not terribly likely to get fixed, among the many other priorities we have.
So yeah, quirky but explainable at least.