A long shot, but the old LL diesels used to come with a sheet for replacement parts, with prices listed. The entire list of parts equaled the total MSRP of the loco, so I figured it represented approximate cost of producing each component. I don't have any LL locos left, but if you did, it would provide a nice reference. Kato has a lot of parts on their website, and maybe they have the chassis price, and with a little math, you could calculate as a % of total loco price.