The price to make those arrows it's cheap but the problem doesn't rely on the price of the arrows but on the arrows itself.
There's no much space to develop here. Fire arrows are to OP against stone, acting like their working on a wood surface, and they MUST be nerfed in that sense.
People are just not using trebuchets and other items, because fire arrows are cheap and can raze stone stuff.
There was a massive fight on my base and I took some screenshots after.
I rest my case. Someone has to do something about this, I'll be happy to know if any of the devs are already aware of this issue.