E-nites are for resort guests only who purchase a ticket to stay in park after closing to ride the "E" ticket rides. (When WDW opened -rides costs certain tickets A for the easy ones, E for the best ones.) Rides that are open are those that usually have very long lines during the day like Buzz, Space Mountain, etc.
I believe the cost of the ticket is aroun 10 -12 dollars - someone please correct me on that if I am wrong.