In Onondaga County, you can go online to www.Ongov.net,
Simply click on the Real Property Tax Services tab, then on the left click on Property Tax Information Search, the click on the highlighted text that says Click Here (for Onondaga County Properties).
You will be brought to a Parcel Search page where you will type in the street # and then the street name, click Search and you will have the Property Details page.
From there you can click on tab "Report" on the left hand side (5th one down) and there you will see under "Sales" when and how much the owners paid for the house.
However, sometimes this information is so old that it will be necessary for you to call the particular town clerk to obtain this information.
Either way, it is public information and easy to get (once you know how). Hope this helps! Feel free to contact me for any help with this or any other Real Estate related matter at (315) 656-8300 - Julianne O'Reilly - - http://www.SyracuseListings.com