What is the going rate to have someone negotiate a mortgage modification for you?

I’ve been approached by a company that negotiates home mortgage modifications. This is not a refinance. What they do is approach the holder of your existing mortgage and negotiate new terms—which, in my case, would to change my adjustable rate mortgage to one with a lower fixed rate (probably over 40 years).

Apparently, the sub-prime crisis is motivating a lot of lenders to restructure their loans on more favorable terms so as to reduce the risk of foreclosure. The catch is this company wants $4,000 to do something I could theoretically do myself. The thing is, I might not be able to get as good a deal as they can, since they do this all day long and presumably have some expertise. I suspect they might be willing to come down on their fee if I asked them.

So my questions are, 1.) Are these offers legit, or are they just another predatory scam? 2.) Do they really get you a better deal than you can get yourself? and 3.) If they can, what is a reasonable fee for this service?