API for historical housing prices I'm looking for an (ideally free) API that would have time series avg/median housing prices by zip code or city/state. 

Quandl almost fits the bill, but it returns inconsistent results across different zip codes and the data is not as up to date as I'd like (it's mid November, and the last month is August).

I also looked at Zillow, but storing their data is against TOS, and at 1,000 calls daily--it would take forever to pull in the necessary data.

Any suggestions (even if they aren't free) would be much appreciated!
The United States Census Bureau has many free housing datasets (some of which are updated more than once every 10 years). There is an API for American Community Survey 1 Year Data that includes housing data. There are raw data sets at American Fact Finder.