Well let me be the totally irresponsible one here....

It is true that without knowing anything about your case, I can't say if it's worth $1 or $1 billion. That being said..I would guess....

If they offered $25k, I would guess they are prepared to give up $35k - it all depends on how stupid they think you are. So if you feel $35k is fair, you should counter at $50k. Or you can get a lawyer - who may get you the full $50k and after his fees, you will get $30K. Or...

Hire a lawyer and negotiate his fee on the amount over $25k. Logic being is that you have already secured a payoff of $25k and most likely could get $35k without any assistance. Therefore the lawyers fee should only be based on anything over the $35k. They should not profit from the work you've done.