A good example of buying a 70 Duster done rather than building one

You couldn't build one for $20 large unless you can do most of the work yourself. Ya, if you look close there's some screwy details but if it was perfectly restored or perfect original it would sell for $40,000 or more.
I watch friends building cars up here and they are at $20k US with just the body work done on the rusty shell they started with...