Howdy yohanaton,
What you could do is only create a new Role & maybe a Capability for submitting events from the community form. Then using the WP API you would only allow users on the Community Events Submission page if they have the proper permission.
From there it would be up to you as to how you charge them for access. You might use a digital shopping cart plugin like EDD or WooCommerce. I bet you one of those would even allow you to directly sell user_roles, possibly via an addon. Then it will be automated.
This might sound like Greek to you. To do what you want is a solid customization, and thus requires a developer with a good knowledge of the WP API. So if that does not describe you, you will likely have to hire someone. If you do not know anyone whom you can hire, we actually keep a list of freelancers who are quite capable of making such changes on your behalf. You can obtain this list by emailing [email protected] and requesting it.
Does that make sense? Will that work for you? Please let me know. Cheers!
– Brook