The entry to Petra is not cheap, but it is worth every dinar. A one-day ticket costs about 50 JOD, a two-day ticket about 55 JOD, and a three-day ticket about 60 JOD.
The ticket includes entry to the site, the Petra Museum and the Petra by Night experience. The Jordan Pass, which includes the visa and entry to many sites, includes Petra.
It is a good idea to buy the Jordan Pass before you travel, as it saves money and time. The ticket is checked at the entrance, and you can enter and leave the site on the same day.
For a traveller, the Petra ticket is a great value. Visitors can plan their visit, and full package tours include the entry.