Madaba is about a half hour from Amman. There are frequent minibuses each way (about 500 fils each way). A taxi is a good option, especially if you're in a group. The cost depends on your bargain abilities but it can go from JD 8 - 12. If you are coming into Madaba from Amman, make sure you get off the bus on the 'Kings Highway' before getting to the bus terminal as it is now located east of the town and you'll need a taxi to get to the centre. The city is also only 25 Km from Queen Alia International airport, making it the ideal place to start and end your trip to Jordan.