Build Database of All 2009 & 2010 Real Estate Sales in USA

Every County in the USA record property sales for that county. This is done by the Tax Assessor's office for that county. All or most of these counties have a website that you can search and find individual properties. Some have full database download. This is free, public data but it is not in a format that I can use. I would like to know if someone can spyder these websites and build a DB with all this information (specific fields required will be provided). I am not sure what the possibilities are to get this data but I have the list of all the counties with websites with this data. Please give me a proposal to do this work. What approach would you use to get the data. If this is possible I would like to get started ASAP. I will need to have the ability to repeat this extraction at least once a year or more frequently.