It's a nice one mate,
For the UK market you I'd offer around £2000 at least.
If I was you though, I'd check out the market in the States. All depends if "Fee" is a relevant word in relation to legal claims. Plus do they have a similar legal process where the losing legal team has to pay the winners costs, otherwise no one is going to offer "no fee".
You'll probably need to do a bit of digging into their claims process, because if it is relevant then you could be looking at £20,000+
Especially with the way they sue each other for fun.