Yup, the quarters will need to be replaced, probably the trunk and floor pans as well. Can't really tell about the roof, but I'd want to crawl underneath and make sure the framerails were solid before I bought it...
Also FYI, I bought my running, driving '72 for 11k. Thats US $, but its all about the same now. It has a small hole in the floorpan and a small soft spot in the driver's rear rail, but the rust on that car looks much worse. Mine may take a small patch or two on the doglegs of the fenders, but no full quarter or fender replacement. I'd want to work the owner down from that price, or keep looking...