I have to plant 33 5-6ft tall abervities. the root ball is about 12in. in diamiter and 12in. deep. Will an 18in. auger be ok, or should I use a 24in? Does $30 per plant sound resonable? Total $990. The trees are already delivered and paid for. I will be renting a dingo w/ auger for $225. How long can I expect this to take? It will be me and one helper. The ground where I will be digging is flat and seems like it will be easy digging.