I'm far from an expert on this topic, but did a quick search on e-Bay and found that there aren't a lot of original blueprints for cars out there (lots of repros though). There are a few 1920 Pierce arrow limo originals with a buy it now price of about $35, and a number of 1920 Autocar blueprints starting at $14.99 up (depending on condition).
I'd hope that Pantera blueprints would fetch more, but like I said, I'm no expert.
If you have a figure in mind and want to PM me, if it's reasonable I'd be interested - you're right, they would probably look nice framed.
Thanks!
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