There is only one way to estimate the price you should offer for an existing home. Compare the asking price, renovation costs, and probable deferred maintenance costs to the fixed base price of new construction home. This is called establishing a price baseline when shopping for a resale.
Our advice: If you plan to purchase an existing home for around say $500,000, visit a $500,000 new construction home first so you can see, touch and feel how you can live for $500,000.
The new home might not be the location you want but you might fall in love with the floorplan. The resale may be in the location you want, and you may be willing to pay whatever it takes to renovate the resale. Either way, by knowing what your money will buy, will help you make a faster, more confident offer for the resale.