I know the old 5 windows are revered out here. I think Rogers idea of keeping the body intact and just lowering it would be o.k. with the Bow Tie boys, but start chopping on one of those is enough to insight a riot! Also as you already know they go for a fortune! I remember in the old days of my youth you could get an old one with a 4 cylinder 3 on the tree for about 500 bucks running! It's amazing what they demand now!
I'd watch Craigslist, but more than that I'd freestyle pick so to speak, and drive the old country back roads looking for one sitting in a field or driveway and then cautiously approach the residence asking if they'd consider selling it, not mentioning "Rat Rod" per say, just you want to fix it up for a daily driver.