For fixing up, it varies from house-to-house depending on condition.
Pick a couple of houses that you see.
Then use the worksheet that is linked herewith, fill in the appropriate blanks, and go to your local Home Depot or Lowe's and work up the costs of your materials. You may have to call a couple of contractors, too, if the house needs foundation work, roofing, or something else that requires someone with the know-how and equipment.
I have seen rehab properties that can be repaired for as little as 5000.00 others that because of strucural issues need to be torn down and the seller is trying to pass that cost to a buyer.
I currently have a side by side duples listed that may take 25-30,000 to rehab. The property is being offered for 8000.00 and should return about 1000.00 after repairs. It is not selling because about 1/3 of the neighborhood is boarded up.
Rememmber you may be able to come up with averages but real estate is a case by case basis.