I have to agree with you that most of these modern tractors willhave been melted down and come back as something different a couple of times while an old AC will still be running. I am working on a WD that I plan on having outlive me.
As far as the cost, I agree with the others here, It could cost you 3 grand. However spread out over several years and the fun and satisfaction, what could be better. You could drink up that much beer, and have nothing to show for it, or easily spend that much each winter skiing, and not have near as much fun, maybe break a leg too and be out of work costing you more. Do like someone said, one part at a time, if you get temporarily stuck on one thing set it aside for a while and go on to something else while you figure out what to do with the first one. It isn't a race, the longer it takes the more time you get to have fun working on it. The guys here will help you out with advise when you need it, gop for it!