Well you can't yet smith addy plates, but you can make steel, and mithril at 68, so,
Buy 5k steel bars, forge into 1k platbodies,(4 mil net loss) then
Buy 2k mith bars, and forge into 400 mith plates,(2mil net loss)
You should definately be there, and it will cost around 6mil if you sell or alch the plates (going all steel is cheaper if you avoid mith)