I work alot with investors, "flippers",and home buyers looking for fixer-uppers for themselves. Generally, Unless there are already double pane, low-e windows in place, we assume the windows, together with fixtures, heating, cooling, roof and soft floor coverings have to be replaced. If it turns out they don't, it is a plus! When buying a fixer, you need to consider worst case scenario on repairs, consider location, functionality of floor plan, changes and additions possible for the floor plan, Square footage, condition and orientation of property, zoning, design of home, condition of walls, age of home, plumbing and electric, and the neighborhood.
Calculate what the finished value of the home will be. If you are doing this for investment, you need to back out closing costs on resale, profit, and expected cost of repairs. If repairs are extensive, back out at least 1/2 annual taxes. What is left is what the purchase price of the property should be.
If you are buying as a primary residence, you can out-bid the investors and still get an awesome deal on a home with a finished price below market.
If you need help with this, I would be glad to assist.