There are also long distance coach services from Sevilla to Madrid.
http://www.alsa.es operate several services daily from Seville to Madrid Estacion Sur. Transit time is currently 9 hours but the price of a single is € 35,34.
http://www.socibus.es also operate a similar service.
Transit takes between 6 and 6 1/2 hours and the fare is € 19.25 according to their website.
I used their overnight service from Madrid to Seville a couple of years ago. Not luxurious but perfectly adequate.
