Same answer -
You can go to the county and find that information on the Tax record; or your realtor will be able to tell you. If you post the address here, we might be able to help you.
or Zillow works too. it shows when the house was bought and how much it was - Go to the Zesimates and Charts, it will show you the last sold price (the owner's purchase price)
However, to save another question - don't go with their estimate, it's not accurate yet (another toopic) - you definitely need to talk to a Realtor for an accurate comp.
A side comment - what the seller paid for the house has very little to do with the market price of the house.
I guess that some MLS systems require disclosure of the actual purchase price, but I see $1 recorded in MLS frequently as a sales price.
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A Realtor will be able to help you quickly IF the property was sold through the MLS system, if not, then they will have access to some tax records that you also have access to, but they can still typically find it sooner since they know what they are looking for. Note that the Realtors don't have the selling price until AFTER the home actually closes unless they were a part of the transaction and even then they legally can' give it out until after closing, since if the home doesn't close they have put the seller at an unfair advantage with a second contract on the home if they tell the public what he accepted with the first contract.
Let me know if you'd like help with finding out what something sold for.