last week i sold 2500 lbs of cast iron. it went in as mixed yard cast at .145/#. it was worth it for me to pay a buddy of mine to help me load it all.
The problem is that a load like that is rare for me. its hard to get my hands on that much iron on a consistent basis. if its worth your labor and gas, go for it. otherwise try to offer less and negotiate. they might be willing to budge on the price