Karen, you have received advice from a number of appraisers who are generally considered to be among the best of the best. Free advice at that, so you're getting a really good deal.
I used to specialize in all things "diminution of value" related, and have substantial experience with condemnation and inverse condemnation. I have performed a decent number of appraisals for title companies pertaining to diminution related to title defects.
I'm a bit of a perfectionist, but more so a pragmatist. Based solely upon the information you have provided, it is my personal, non-lawyer opinion that you are on the right track.
The title company will likely be the path of least resistance - you should be able to adjudicate or settle outside of federal court, and, if the easement is, in fact, a specifically scheduled item, the odds are probably in your favor.
The inability to finance your home may well have a very substantial adverse impact upon both the value and the marketability of your home. This type of analysis is generally more tedious than complex, and usually requires many hours of research and verification. My fees for this type of assignment typically ranged from a low of eight or nine thousand up to around thirty thousand dollars, possibly a little more. Your lawyer's fees will likely be at least around the upper end of that spectrum, quite possibly even double that. Those fees may or may not be recoverable, depending upon the laws in your state, about which I know nothing. As has been mentioned, previously, your attorney should be able to recommend one or more appraisers competent to do this assignment. If your attorney cannot do that, you NEED to change attorneys. The best appraiser in the world will be useless unless your attorney is truly an expert in these types of cases. If you need to change attorneys, one of the questions you might want to ask is the prospective attorney's win ratio. I wouldn't touch anyone under seventy to eighty percent, minimum. Best of luck to you!