I've seen many posts about selling leads to lawyers and one of the themes of the posts seems to be that you can ask for big money because they make big money. The other assumption or business idea is that you can sell the lead based on the fee or award that the lead may bring.
(I guess I should say at this point - although I've mentioned it before - I'm a Director of Marketing for a Law Firm. I don't say this to put myself out there as any kind of expert, but simply because my work has allowed me to understand the laws as they apply to "leads" and since we purchase leads I can tell you what the actual cost is. I know a couple of people personally who could have saved a lot of time and money if they knew this stuff.)
Cost of leads:
Bankruptcy: 20 - 60
Accident/Injury: 18 - 50
Divorce/Family Law: 18 - 40
Medical Malpractice: 20 - 60
I can't speak to every type of lead about it's cost, but the vast majority fall into this range.
As far as the idea of a percentage of fee, it's simply illegal and many attorneys have lost their license doing this. It's known as fee splitting and it's the same law in all 50 states. (By the way....this applies to US law firms...laws may be very different elsewhere)
In the last couple of days I've spoken to a couple of people who were in the process of building a business plan around unrealistic expectations of how much they would be able to sell leads for.....hence, the reason for the post.