Septic fields, am I being ripped off?

We kicked them off the job. They tried to get me to pay for the machine work, so I said we could trade for the yard they tore up since we never even had a contract. They let their issue go.
We had another guy come in and give us a quote of $15K, and he was recommended to us. We're going to get a few more quotes and see where we end up.