Leah's resource is one worthy of taking a look at....we have used it frequently and it has helped many people by establishing basic plans before becoming involved with a contractor. Another benefit of this source is that it provides a good basis for establishing the return value on your repair investment. This can serve as a good tool for prioritorizing projects.
Ron's point about being careful about not over simplifying remodeling expenses is one to keep in mind. Remember that any "cost calculator" is a very basic resource with a variable that should be considered.
There will be major differences in costs based on products and materials chosen, and whether or not you are capable of doing some of the repairs yourself. Then be sure to add in the cost for permits. Good luck!
I would not trust any body or anything that purported to simplify it.
If you are looking for a guideline; just take the BIG ticket items, like roof, HVAC, exterior/interior paint, remodel kitchen, and add those up.
If you are looking for accuracy; get a pro to work up an estimate.
Like everything; do it right, or don't do it.
Good luck and may God bless
What you are looking for is Knowledge all there is on line is Information. Don't try to do it alone.. get a good team around you that you can trust and has skills aligned with your goals. Asking for an online cost estimator to me is like a brain surgeon asking a Blog site on nutrition for how to operate on a brain. If you are buying a fixer upper to live in as your primary residence then get a good Real Estate Broker and Loan Broker at a minimum. On top of that I would suggest a General Contractor that you can trust at a minimum. If this is a fixer upper for profit then you need to have a lot more team on your side including an accountant etc.
For fun and INFORMATION you can try the website that I attached but for KNOWLEDGE you need the experience of professionals.
Yes, there are online remodeling calculators and simple cost lists out there. Marshall & Swift is pretty good. I used it when I was an appraiser. However, your best bet is to get 2 or 3 estimates for your remodel project. Contact licensed, bonded general contractors who work in your neighborhood and who can give you an estimate for everything you want to do in your project. They will have the most accurate costs for remodeling.
The more general the information, the less reliable it will be. I've looked at the remodeling site Leah suggested and find it interesting, but to imagine the entire west coast would see the same returns is pretty hard to imagine.
Your best bet will be to spend some time pricing out fixtures and materials yourself to get a base of knowledge to work from and then get some quotes from professionals. The more work you can do yourself, the more you may save but you need to have professionals do anything relating to bearing walls or structural issues.
Other good resource is Marshall & Swift: http://www.marshallswift.com/
Good luck with your project!
Just to add a little to the comments you already received, remodeling costs vary hugely depending on the condition and age of the property.
There is a difference between remodeling and updating, and many people confuse the two in their language. Remodeling really means changing the structure and doing work that usually requires a permit. Updating is simply adding new paint, cabinets, appliances - that kind of work.
If you are truly doing remodeling, it runs about the same as new construction, which is $180 to $200 per square foot. In remodeling, there is often a demolition cost.
I can refer you to some outstanding remodeling contractors, and who I would refer depends on the scope of your job and the level of quality you are planning.
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,