1) Your concept of screening coders for talent is important, only accept people who can get things done.
2.) Only charge developers a monthly fee. The collective fees should be enough to cover the cost of an ongoing marketing campaign to attract the right businesses and entrepreneurs.
3.) Educate businesses and single entrepreneurs about the cost of projects, and cost of talent and explain trade offs for paying less. Experienced coders may cost more, but they have the experience can work faster, less learning on job....coders who charge less may be less experience, in different time zone, not so fluent in native language, etc. Provide rough estimates based on info on past projects. i.e. Angry brids cost about $150,000 to create. (http://www.develop-online.net/news/37242/Angry-Birds-cost-Ro... )
4.) The education is important and it provides prescreen of potential clients, only accept projects that fall within reasonable guidelines.
5.) Do not charge businesses a monthly fee. as mentioned by MatthewB "If it takes any more than a month to find a dev, there's something wrong with your system." Once developer has been found, charge business/entrepreneur fee per projects because you're providing technical screening service.
Note: So the idea is to take some elements of successful services like elance, etc and raise the bar. setting up useful guidelines and an effective marketing campaign will not be easy.