Aircraft Appraisals
There are aircraft appraisers out there. I found one for an estate settlement involving a certified airplane. But I believe he said he had appraised experimentals too. I found him through an EAA chapter yahoo group. He also had owned an RV-9A so that also would be a plus. Of course there's a fee involved, but compared to the value of an airplane it might be worth it for you.
Send me a Private Message (upper right corner of this screen) and I can give you more info if you're interested. Not sure if he would travel to Virginia but he is in the Nashville, TN area.
P.S. I just noticed you asked for an online service. As is typical, I didn't read the original post slowly. You may totally disregard everything I posted above.