I would anticipate that costs will vary widely.  How complicated is the site?  What type of effort is required for the file review? How much investigation is "enough"? What types of measures are implemented?  What ongoing monitoring obligations are selected and how will those be funded?  Those are just a few of the questions that will shape that discussion.

Consulting firms and clients will need to determine the arrangement that makes the most sense to them.  While it may test the comfort level of many, I'm sure at the end of the day many different types of arrangements will be made, and that all parties will benefit. There is a great opportunity for creativity here.