The OWNCOST variable of homeowner expenses is listed as available for the 1980 Census, but much of the data is missing. Over 13 million owner households have missing cost data, or about one quarter of all owner households, severely limiting the usefulness of the remaining data. Is there a reason why this data is missing and is it available anywhere else? All the 1980 Census samples have the same problem.
I am not sure why there are so many missing values for OWNCOST in the 1980 samples, however this is reflected in the original Census Bureau PUMS files as well. I would recommend constructing OWNCOST from its component parts as described in User Note 2 of the 1980 PUMS Codebook (pdf page 15) for the entire sample. The following is the correspondents between Original Census Variable Names and IPUMS-USA Variable Names:
Make sure you account for the codes that represent non-response (recoding them to zero). You will then need to separate households with codes of zero that should not be in the questions universe. Doing this I end up with 10,133 owner occupied households that have OWNCOST==0 (which is also strange as we would not expect any eligible households to have zero monthly cost). You may wish to contact the Census Bureau directly, referencing the variables by their original Census name, and ask if this is a known issue.
I hope this helps.