The M795 projectile is about $500, so that sounds about right. Just the “dumb” shells are fairly cheap. Once you start adding guidance and specialized fuses, the price starts to get cranked up. I don’t know too much about artillery though, but the powder charges should be fairly cheap as well.

I would have to start digging to find what the real prices are, but it’s probably still in the ballpark. The real cost is in the equipment.