Offer seems low to me ?. Only issue with fixing her up is when to stop. With paint work comes body work, both of which can turn into major $$. Same with motor work - once it's out hard not to add a few " bells & whistles ". Once shes all painted up needs new wheels & tire *G*
But...on the plus side, even if you put 10k into it, you will have a great looking, rare, & reliable daily driver. Just look at what new, bare bones pickups sell for these days.