While I completely agree that it will not be cheap to fix; if you have done the cars you mentioned (the Vettes) and such and have a good source of knowledgeable buddies, you can possibly build this car into something fair for a reasonable price. By reasonable I mean like $20-$30K depending on how nice and high speed you want to go and do all the work yourself; shop for deals on the needed components, save what you can, etc. You are going to need someone who is a Mopar guy or spend a lot of time on here as Mopars are vastly different than Vettes, Chevys, etc. If you make the mistake of using some GM or ford components like brake boosters, radiators, etc on that car it will ruin the value and be shunned by much of the Mopar community.
what everyone (or most) is trying to tell you is YES the car can be saved, rebuilt and made into a cool car. No it is not rare within the Mopar community, Yes it is still cool. My personal advice; if you love Challengers (you will need this love to sustain you through what is going to be a painful, trying, expensive endeavor), buy it for as cheap as you can get it, build it into whatever you want it to be (restored, restomod, G machine, etc) and enjoy it. Are you going to be able to flip it at BJ for 500K... NO you are not. You need to build it to enjoy it. If you are thinking of building it to flip it and make money, good luck with that.