Is there a quick way to estimate repair costs?

[Stacey Olson]

It looks like I may have a meeting (my first with any motivated seller :-D) tomorrow with a highly motivated seller.  

The question: Is there a way to do a rough estimate of repair costs on a SFR? We're going with the 70% rule (70% of ARV minus repair costs).

The details (those we know, anyway): Partially gutted 1,546 sf home; 4 Beds, 2 baths. Assuming the foundation is sound. Roof appears to have some life left in it. Windows need replacing, exterior needs paint. No drywall in interior. lacking all fixtures and appliances. 

We just need a very rough estimate so that we can come up with a ballpark figure.

Thanks in advance for your help!

Stacey, Tacoma, WA