I just realized my last comment the companies I mentioned do not offer 80% blanks. Any one know of companies who do that we can try to get a group buy going?
Sarco has them occasionally, as well as castings in various stages of completion. Someone on weaponeer built one from such a casting: http://www.weaponeer.net/forum/forum_posts.asp?TID=10185&PN=1
EDIT: Sarco has some castings in stock for $30. Keep in mind these require a considerable amount of machining. http://www.e-sarcoinc.com/widebody191145framecastings-3.aspx