Looking for credit/currency plugin - any recommendations?

[Meerski]

Hello,

I've created following forum: forums.gameofthrones.ws

I would like to introduce a currency system for following purposes:

1. I've designed 45 avatars which they would be able to unlock with there earned credits
2. They can buy "lottery tickets" , which cost X credits, they should be able to buy as many as possible (if they got the credits). At the end of the week we select a winner.

The credits/currency can be earned by:

1. posting: 1 post = 1 credit
2. opening a topic: 1 topic = 3 credits
3. buying credits: 100 credits = 0,99$ (for example)

Do there already exist a similar plugin?

Which ones would you recommend for my forum anyway?

Thanks!

Dries