Be prepared to walk and climb, a lot! Petra is a historical city that dates back thousands of years. It's mostly noted for the iconic Treasury but there are a slew of other ruins, canyons and cliffs that beckon to be explored. Like any city, its attractions are scattered about. This results in you spending hours hiking up and down as you traverse this vast site. There is the option to ride horses, camels and donkeys to get around, however, if you are on a cheap budget it's better to strap on a good pair on shoes and grab a water bottle.
Petra offers 1, 2 and 3 day tickets. At a hurried pace many have been able to complete Petra in 1 day. Yet the price for the 2 or 3 day ticket is not that much more expensive. If your budget allows, try for at least the 2 day pass. Plan to bring lots of water and some food to snack on or even your lunch. Buying these items inside the site are more expensive.
Nobody visits Petra without seeing other regions of Jordan. Depending on your departure city, plane tickets to Amman can be pricey. Some opt to fly into Tel Aviv and then cross the border, thus resulting in an extended holiday. If you do this, don't forget to add into your budget the Israel exiting fee (paid at the The Jordan River Crossing or Sheikh Hussein Bridge). From Amman and Aqaba there are daily buses and shared mini buses that make the trip to Petra; these are the cheapest way to get there from these cities.
Lodging and transportation is very cheap in Jordan, yet the price of food might be a little more than what you expected. Petra's sites are truly awe-inspiring and mind blowing. Stop putting this trip off and go visit Petra!