Pay to join mod wanted

[Doug Nelson]

I like how some sites require a nominal fee ($1 or so) to join. I think this would cut down a lot on spam. Is there a mod that can do this?

Subscriptions won't work, because I want it as an option at registration, so they can say yes and join, or no and join with less priveledges. Preferably a button or link on the registration page. Subscription require that they've already joined.