Their decision should be purely based on market analysis, loss tolerances, and congressional hearings!

Or what is the minimum cash flow you can tolerate before its not worth keeping the property?

Both were effective for me, but then I have a higher tolerance for trivia than many.

You can tweak that number depending on your personal risk tolerance.

If you have that kind of risk tolerance, you should complete it and if you don't set your house on fire in the future, good stuff you've forever saved yourself money on an electrician.

You would need to find out what the appraised values of your grandparents and aunts property with home would sell for and get a quote on the building of a similar home on your land would cost.There are many factors to be considered in building not the least of which are money to build, experience and stress tolerance.

If the numbers fall within a certain tolerance I take it the step further and run a full scale financial assessment. 

Appreciation is a wonderful thing but you're not always guaranteed with the appreciation nor are you guaranteed with the income on a monthly basis it's just what you choose and it's a matter of your risk tolerance . 

I wouldn't call it overpaying, simply its above where your numbers/risk tolerance allows you to be based on your calculations.Now if you've tightened up your numbers as much as possible and are confident they are accurate and still cannot justify these prices, the other option like @Mike B. stated is playing the waiting game and finding something off market.

As long as your wife is tolerable and doesn't complain to much about the less than ideal living situation, it is a great way to break into investing.