it wouldn't.
i'd rate it a 6,000 GP flat cost missile weapon enchantment
it's a feat an archer would take anyway
at best, you are opening up ranged combat to non-archers
Just making a point that duplicating precise shot as a weapon enchantment is equivalent to more than just a single feat (closer to two actually), since point blank shot is a prerequisite that is not very useful except as part of the path to precise shot.
Is it unbalancing, probably not. I would say it isn't a cheap enchantment though. I would say making it a +3 equivalent would be appropriate. I suppose one could argue it as a +2 instead of a +3, but when making new things, I find it best to be conservative in regards to power level and liberal in regards to flavor. You can always power it up a bit (make it a +2) later if it turns out to be underpowered. Also, players are almost always happy with that scenario, whereas they would be significantly less happy if you tell them that their +2 Precision Longbow is now a +1 Precision Longbow because you've decided that the Precision enchantment is too powerful.
Just my 2 cp.