The only way I know of without using an agent to search the Multiple Listing Service data would be to go the county court house on the third floor is the records room. Take the address of every house in your neighborhood and search for the deed and mortgage for each one. The mortgage amount is on the mortgage and you can determine the amount of the down payment by the tax stamp and recording fees on the deed. The ladies who work there can show you how. Of course, the only pertinent data would be for the ones that sold most recently, as far as telling what the current market is.
Another thing to think about, depending on your purpose, is to ask an agent for help. Many will answer your questions with no obligation to you. We do a lot of free work as a way of developing good will, so that if not now, perhaps sometime in the future, you or someone you know may decide they need to employ the services of a professional. Best of luck.