You are right, to get accurate information it does take tedious searching. Sometimes tax information can be pulled on a specific property but it is not always accurate. Most sites do not take into consideration the condition of the properties as well as the homes around the properties and that is where they have flaws as this is very important information for value.
Having been a realtor for 25 years I have seen how condition is as important as price but that is not often reflected on sites. A local realtor more often has knowledge about condition and values in specific areas as they have been in those properties and have seen how the area's values change over the years.
It is best to contact a local realtor for best information.
And, you can call/email me for questions or more information. Very best to you