#3985 needs fairly significant boiler work. Some will say "oh no it doesn't" but yes, it does. And I'm not just referring to the superheater units - yes, it would need a new set of those. Never mind what happened to her old units - the reality is they're gone and would require replacement. As to the cost - you never really know until you get into it, but you can pretty much bet the boiler would cost $1m +, especially done the way UP does it now.
I think the running gear is in pretty decent shape but knowing Ed he would go through it anyway - add another $1m +. Then there's the tender that #4014 is using now - more $$$ to get #4014's tender usable and return #3985's, which I understand isn't in pristine condition either.
Any way you look at it these machines are not a cheap undertaking. While I, too, always liked #3985 and would like to see her run again, its difficult to see how it could be justified based on what UP uses the engines for. Two big locomotives is more than enough. Lets be happy with what we've got.