Not Bronco, but I remember going through the glove box of a '76 Plymouth Fury I grew up with. Found the original paperwork. Sold for $3300, $300 down and financed for 3 years.
The '77 F250 I recently sold had MSRP on the title of $4667, it was a well optioned 2WD XLT Lariat Camper Special big block.
Broncos were expensive when new.