Dear Anil,
The first step is that you create a system where the user can purchase credits with CRED and CRED commerce plugins.
Afterwards, you can use a View to show the posts to the user with a button to make it featured. You would only show this button if the user has credits available. This button would be linked to another CRED form that makes the post featured.
I imagine you will need to write some custom code to glue everything together. For example, discounting credits needs to be done using the cred_save_data hook explained here:
http://wp-types.com/documentation/user-guides/cred-api/#csd
I suggest that you start developing the first step and let us know any questions that come up in the way.
Regards,
Caridad