Sorry I cannot offer specifics on your question. I looked into building one several years ago, but decided to build a boat instead.
I am sure you have already seen it, but there is a link on the Glen-L RV site about estimating costs.
Again, I just wanted to point out the obvious. From what I remember, the estimating quantities were pretty good at getting the shell finished. However, the interior obviously determines to a large extent the cost of the trailer. Good luck on the build. There does not seem to be a ton of people building trailers, but we enjoy pictures. I have one of these on the "next build" list.