2 key things IMO to point out:
1. If you get an appraisal,it needs to be sales comps of pipeline ROWs, not price per acre of the land. There is a recent case where this very issue was argued.
The weakness of our situation is that it can be expropriated
This is true. However, there is a statute that states if the landowner's eventual award from judge/jury is more than the highest offer by the expropriator, you can receive all atty fees and costs of bringing it to trial. So its not quite as big of a deal to go to court if you feel confident about your demand compared to their offer.