I would seek the counsel of Jeff Dowler, CRS, Nina Hollander and Lyn Sims as a starting point. 

I believe that Brivity has a component that will do this for you.

I would second what Wayne Martin advised

Tongue in cheek here ... send people to the Z Devil. 

That is not something I use in an automated way. I prepare home value reports for clients who are selling. 

I am interested as well, I am not sure it exists.

A so called agent with no bio, blogs or any type of info asked about a product and gets a detailed reply about a product from another so called agent with no bio, blogs or info. We just got spammed with a product placement.

Looking for electronics to do your job is like thinking the zestimate is accurate.  Build a landing page and do a CMA for them if they give you the info.

I have not located one that works well, and ask homeowners to call me for their home value.

Valuations are a tricky breed to be accurate without actually stepping foot on and in the property. You might be able to construct a usable one for a local niche market although I wou;d be wary to use any AVM for a blanket result. History is a good lesson so if we look at Zillow's progress to accommodate this since 2006 their accuracy can only continue with a disclaimer of within 5% of sale price between 70% and 90% which does not impress me. I didn't say it's easy!   

There is a section in Cloud CMA that does this. Problem is it 'does it' badly. In my area there are mixes of townhouse & homes & the system can't seem to figure out the difference. Not very accurate. I've stopped using it years ago.

R/max has one also in it's Booj site but I can't remember why I don't use that one either.

So I too am looking for something of value. Hope we get some good answers.

Check out HomeBot. They provide the home's value and other useful information that will help users save on their mortgage.