Fun fact: I am a Data Engineer.

I would also recommend the following data sites for not only Jacksonville but also for other cities and states.U.S.

Where is the best place to look for market data to help guide me in pinning down a purchase price?

If you want a software program off the shelf that will generate pages and pages of data then buy a software program for this.

Also, you would need to input a tremendous of data if you want it to determine highest and best use.Sound like you are the "newbie catch-22" that nearly every profession runs into. 

Poke around in Zillow's recent home sales data and you'll eventually start to see patterns.

The data you compile this way is not as valuable as lease info with a close proximity to your building, but it's a place to start. 

Quality of the local real estate market Market Research Real estate market analysis involves studying the current market and predicting future trends.Review of local and regional trends in the real estate market Analysis of local demographics Assessment of local economic conditions Project Goals Goals provide a clear direction for the progress, real estate investment goals include, maximizing profits, increasing ROI, diversifying portfolios, and providing affordable housing.Project Scope Setting a budget and timeline is essential to define the scope of any investment project.Financial Analysis Financial analysis and key performance indicators provide crucial data to assess investment feasibility and make well-informed decisions in real estate investments.

It will probably ask you for the tenant's birthdate, but you may be able to get the civil data without that (at least that's how it works in my county).

We spent a lot of time and effort on studying the market data and purchasing review-based data from top performing properties and from super-hosts all over the country.