You'd save so much money taking the bus instead!
You could even rent a car and would still cost you less than half of what that taxi driver asked you for. You get to keep the car for 24 hours too.
Also, you could go with a tour agency and pay 15 to 30 JD.
Are you aware that admission fee to Petra is 50 JD for visitors on tourist visa? Unless you have residency or student card, in that case, you'll pay only 1 JD!