Merging all your unequipped ammo will result in one of the following ammo bundles:
1,803 Arrows [8x1] (+0) Cost: free 1,803 Arrows [8x1] (+0) Cost: $2
The lowest enchantments from each group will be used in the final bundles if you pick the free option.
When merging bundles of equal ammo, why is there a choice between free and not-free? Is it just in case somebody is wanting to donate for the service?