Question - Answer script with payment system

I need a simple script. On the main page there would be a big box for questions. A client asks a question and it forwards him to a sign-up page(really simple, just name and email) and after a successful sign-up, it forwards him to the members section to his ticket thread. So pretty much every member who signs up will have his unique ticket system inside where he can ask questions. I will answer them. And here comes the catch. The client won't be able to see the answer until he pays for a monthly membership, either through paypal or plimus. After payment, the account would become unlocked and answer show up for him. Also, there should be different payment options for different amount of questions per month. For example, if the client pays $10/month, he can ask 2 questions a month, the system just won't allow him to create more than 2 tickets inside. He can upgrade anytime to different pricing options which then allow him to post different amount of questions. He should see it clearly in his members area, how many questions he can ask every month and how many are left. I hope it was clear enough. :)