It's worth what you think it's worth and what he's willing to let it go for. 5.56 is going commercially for over $1 per round at this very moment. But for example, I reload most of my ammo and I do not need to go buy any commercial ammo to shoot right now. So to me, it's not worth $1 per round because I don't need the ammo and will not use it up for that value.
If you need it and would shoot in in the immediate future, you'd spend the cost of your bike for that 2K rounds. If you are not going to shoot it in the near future, it might not be worth that much to you. If you want cash and not ammo, stick to your guns (pun intended) and ask for the money if you don't need or really want the ammo.