I'm only asking if the answer to my questions is possible or exist. if
the answer is yes then I will add tip or ask new question with more
money.
I'm looking for sales and inventory data. I can write programs to
extract data I want, so it can be raw data, data from 1000 different
places or whatever it takes.  I want number of house for sale, price
location (this i would consider inventory). The other information
would be sold properties date, price , location etc.
I would perfer free databases and a mechanized way to interface to retrieve data. 
The answer should include YES or No if possible, is it national, how
many different sources are there.
Thanks