Compared to the cost of magical arrows, adamantine arrows are pretty darn cheap. I'm a miserly player, but there's not much excuse for not having a few on hand. The ability to get through DR is one of the few things archers have going them.Nonlethal Force said:Yeah, but you can't be prepared for everything.
A holy bow with 6 adamantine, 12 silver, and (all the rest) cold iron arrows should get through almost any DR you'll be facing (cheaply).
Now: adamantine arrows of construct slaying... those are expensive (but often worth it since constructs have such low Fort. saves)