As Pat concluded, you can find the relevant bus information on the main bus station. As far as I am concerned the bus ticket and the train ticket cost almost to same from Seville to Granada which was approximately 17 euros, and the train ride is a very comfortable one and there is one in the early morning so you can have the rest of the day for you in Granada.

Also, I would reccomend you to see the "Albaicin" quarter, which is a Jewish settlement in Granada. You will probaby see Alhambra, and Albaicin would be a delight if you will have more time. It is just an uphill climb against the main church downtown which you will find on your trip anyway. It is recomended to walk between narrow streets smelling of fresh food and under grape and fig trees.

Regards, Omer Istanbul; Turkey