Where can you find a property that produces a positive return in that scenario?

In appraisal, there are generally 3 approaches to value - sales comparison, income, & cost.sales comparison approach is typically best and most reliable for residential real estate (4 units or less), income approach becomes more reliable for commercial properties (5+ or more residential units), and cost approach is better suited for newer builds, unique, and/or income producing properties.

Planning is key here to determine your estimated income and how much gain or recapture each property may produce.

There is another way to see the listing prices history if I can't see it on those webs?

For flipping you have to be in a viable market that produces such opportunity. 

He assume each unit produces $200 per month cash flow - $9600 per year.   

That is for, if necessary for us to sell our existing home and move to the number one produced, which will be the first "model home".

Online Auction Sites - Realauction.com, LLCYes you're right, but it's not the only one, there are other platforms depending of the state and the tax lien type (e.g. redeemable has a specific platform), some county has his own system, finally, the main difficulty is to be updated on all upcoming auctions and retrieve the lists to do the research.There are no other platforms for the counties appearing on the Realauction web site. 

That is for, if necessary for us to sell our existing home and move to the number one produced, which will be the first "model home".

A primary home is not an investment, as it's not producing you any return other than appreciation which you have access to only selling or taking out loan.