Looking for offer letter that auto-populates purchase price

Hello, I am jumping back into the mailing to leads game and have recently gotten a few offer letters sent to me for a few properties that I own. I would like to use a similar letter but not sure how to replicate this with a mass mailing and have the correct offer to auto-populate for each address. I am assuming there's a way to connect something like Zillow for example and have the ability to set a percentage of the Zillow value as your offer for each address but can't seem to find the platform that sets all this up. If someone could point me in the right direction I sure would appreciate it!