There is a guy on the boogie board that builds them and there are a couple guys on here that build them just use the search function. The guy on the boogie board, I think he wants around 300 but he does good work.
I bought one for my Mark iv from Zilla and it was a horrible experience. Ended up getting it for cost and shipping and still didn't keep it. It was too tall and just looked wrong. Ended up buying from Mesa directly and was much happier.