What about it?
If you buy a 1996 Superjet, you will pay sales tax (errrm, "use" tax) on the purchase amount.
If you buy an old crappy 550, you will pay the same rate tax on that purchase amount.
The letter I got from Olympia didn't say anything about use tax for the homebuilt VIN.
(Logic would dictate that any materials used to build the hull already had taxes paid on them. But the state wouldn't miss a perfectly good opportunity to get their taxes twice! They do it on used vehicles/boats all the time)
If you "use" a title from another hull, you will present the DOL with that title and the bill of sale. Tax gets figured from the purchase amount.
I imagine that they will charge a similar tax rate on the materials used for the homebuilt. They are pretty adamant about bringing receipts and bills of material. Hummm, it might be cheaper to call my SF a 440.