I am doing research. The web is large. So if you can let me know of companies that provide this service. I am looking in to what kind of fee they charge. based on the number of people who need this service.

0-100 --$?
101-999--$?
1000-5000--$?
over 10,000--$?

What are the least expensive services to use? What are the most expensive?

I would like to have the service accessible through my web page.