Simple its as valuable as he wants it to be. If the company has filed suit and went to court they have already spent $25,000 or more just to file the paperwork. He should ask for the world and slowly go down from there.
In a prior job the company I was with renamed itself. The branding consultants and executive management found the perfect name and started moving forward with all the changes. Then they asked my VP about the websites and such. Of course the name was already registered. After approaching the domain owner about the name he requested $50,000. After haggling the domain owner happily took $20,000. My VP was actually authorized to spend $5 million to acquire that domain.
Point of the story, obviously want that domain badly so your initial amount should be painfully large. Just keep reminding your friend how (s)he felt the day all the legal paperwork was handed to him.