5 free thread creation allowance for all - then move on to charging per thread?

[Make Money?]

Is this possible?

I want to allow ALL users 5 free threads in my classsifieds.. (per year?)

But them move on to charging via PayPal - for the 'power users'?

Does it require a hack? Or just a good understanding of the existing VB3 software options?

Thanks in advance..