There are online cost calculators, and they are not a substitute for, as Arron says, knowledge.
Basically, the best reason to buy a fixer in Seattle is so that you can finish it to your tastes and not have to pay for somebody else's tastes. However, fixers tend to require more than just finish work - they tend to require infrastructure work, which is pretty difficult to estimate, and the return on investment is generally negative. Then, you have to factor in whether the floor plan really lends itself to updating, or if it is functionally and economically obsolete . . .
All the best,