You would need to use a plugin for this. While there is not a plugin that is developed to do both, you should be able to do this easily with two plugins that is released.
The first thing you want to do is install a plugin that allows users to submit articles to you and the one I would use is TDO Mini Forms.
Once you have done this, you then want to find a plugin that disables or hides things in WordPress until a user has paid. For this I would use a plugin like this - http://thewordpresswarrior.com/596/enhanced-paypal-shortcodes.
What you do is add the PayPal short code that the second plugin gives you to hide the page that the submit form is on. Once they have paid, they can submit as normal.
Hopefully that helps a little, I haven't tried it myself but the logic should work out.