The most convenient way to go to Kansi airport is by limousine bus. The ticket can be bought at the limousine bus center besides gakken nara tomigaoka station, north exit or at keihanna plaza if you stay at keihanna. The ticket also can be bought directly on spot if there is still empty seat available. The price for one way ticket is 2050 yen, but for round ticket is cheaper. If you buy for a round ticket open for one week, the price is 3900 yen (if not mistaken), and only 2500 yen for a round ticket during the day.
This day it is easier to take limousine bus. If we usually have to go to keihanna plaza or gakuenmae, we can take the bus from gakken nara tomigaoka bus station. Just do not forget to check the bus schedule.
For bus schedule in Nara, there is an App for iPhone: Nara Bus Navi.