I totally understand your frustration—I had the same problem earlier and couldn’t figure out how to access Maintenance Mode. 
Good news, though! You can now find it directly in the editor.
Here’s how:
Open your project in the editor.
Press the “UPGRADE NOW” button (you’ll see a modal pop up).
In that modal, look for the big “UPGRADE TO MAINTENANCE MODE” button and click it.
That should guide you through the process of paying the $8 and enabling Maintenance Mode. 
I hope this helps! Let me know if you get stuck again.