I believe the train fare would be approximately 20 Euros per person round trip. The problem is that the train will take you about 2 hours each way (it varies depending on the train) plus the waiting time at each end of the journey. By car or bus the trip should take about 90 minutes each way (less if I was driving
). We have also enjoyed simply driving ourselves through Spain using rental cars (once spent a full month driving in Southern Spain) and loved the convenience of having a car. Seville is a wonderful city and should be a great port day.