I'm trying to build a job board of sorts in K2.
Authors can add jobs (K2-items) with their K2-login.

Is it possible to make authors pay to upgrade their job? Example: An author clicks the 'Upgrade'-button on the posted job, selects the upgrade he wants (2 or 3 options), pays $10 and back on the site the status of the job is changed. The status can be an extra field or manually added database cell.

Hope someone can help me out!

Hello,

I think you are looking into a custom solution here.
Akeeba Subscriptions is offering something similar, you can try it out, but I do not think that it fits 100% your needs.