How much to charge for leads?!

I dunno whether this has been discussed before, but yesterday I came up with an idea and I'm currently in the process of making it a reality.

My gut tells me that this has been done before, but anyways I thought about creating websites that generate leads for local business owners.

For example you create a website about dentists in New Jersey, NY, and then on the sidebar you've got an opti-form which asks for the name, phone number and additional information about what the prospect wants to get done.

Lets say you get 20 of these leads each month. Then you put all of the info into Excel spreadsheet and sendit out to dentist with whom you've arranged the deal and who actually works in that area?

Win/Win situation. You rank easily for these local keywords, get traffic and leads, whereas the local business owner only pays for leads that are already qualified.

Watcha think guys?

Lets say that local business charges $500 for the service. Do you think charging $20/lead is a good price? too much? too little?

I mean if you've got one website that gets 20 leads per month ($400/month) then all you need is 25 of these kinds of websites to hit five figures each month and in my humble opinion you can go way beyond 25 because there are so many different industries/cities/towns and etc. You could even take this to the next level and do the same thing for business owners in Germany, France, Spain and so on.

Im wondering if anyone has tried to sell leads to local business owners? Maybe someone at least heard something?

What do you think?

Thanks!