Is this a good “non-profit” idea?

So, an idea I have been kicking around a while is BillableHour.org. Would like to gather some feedback.

It’s a simple listing service for those who provide services that are billable by the hour. Such a person (or company) might be a lawyer, a programmer, or a gardener.

The monthly fee for listing on the site is your hourly rate. The proceeds go to a variety of charities, probably voted on by participants.

Let’s assume the site gathers something of a halo, as a desirable place to be seen by these businesses. Here’s why I like linking the monthly fee to your hourly rate.

It is self-regulating in terms of honesty of rates. If you want to pay less to be listed on the service, by quoting a low rate, you will be screwing yourself. You charge $90/hour but only want to pay us $50/month? Well, now you are quoting your would-be customer a too-low price.

Is this an interesting mechanism? What would it take to grow that halo? To reach a critical mass? Can this compete with other listing sites?

The reason I put “non-profit” in quotes is that I am skeptical of the sustainability of non-profits as organizations. I’d be tempted to run it as a for-profit company that happens to do a lot of charity, and is transparent.

Thanks for your thoughts.