Get one of those tyvek suits and use fine grit "coal slag" for an abrasive. (Black Beauty is a common brand) It's MUCH safer than sand, it's cheap and actually can be reused at least once. Its doesn't dust nearly as bad as sand, it's very hard and leaves good tooth for painting. The problem with rust is what you see is not what you get...It's often only the visible part of what's actually there. Once you start removing metal the project can get out of hand quickly...