2 days ago I took the Airport Limousine Bus from KIX to Kyoto Station. It cost me 4000Y for a return ticket. One way it was something like 2800Y. The travel time was around 80 minutes, in a very clean bus which has English announcements, and a toilet at the rear.
Trains do not cost any cheaper, and they aren't much faster, either. Therefore, I would always choose a bus. ^