Terrific question:
"We pay ½ of shipping charges on all grass seeds, forbes, and small seeded legumes on orders of 50 lbs. or more (UPS, parcel post, or truck freight). UPS is 35% to 50% cheaper if your order totals 200 lbs. or more. The rate on 500 lbs. is cheaper yet and we encourage you to pool your orders with friends or relatives to take advantage of this cheaper rate."
I don't know the actual shipping rate though