That’s an exaggeration. The median price for new construction in 1980 was $64,600. [1] As for existing housing stock, the median home value in 1980 was $47,200. [2] As housing prices are heavily right skewed, the prices of cheap housing is far closer to the median than the price of expensive housing. Based on a cursory overview of some charts, it seems like the bottom 20% of houses are no more that 30% cheaper than the median, putting them in the $30k range.
1975 =/= 1980. Looks like housing went up 64% in those 5 years from the data I already linked.