From Madrid to San Sebastian you may choose between:
1. Regular bus line, with " Continental Auto
" taking about 5 1/2 hours in modern and comfortable coaches. It is also the cheapest option, something less than 4.000 pesetas one way. Around 4 departures daily
Talgo train leaving Madrid about 15.00 hrs daily and also taking about 6 hours. Prices between 5.000-6.000 ptas.
3. Flying is the quickest, and more expensive way, around 40 minutes and 17.000 ptas one way. However, your may find special offers in http://www.iberia.com
From San Sebastian to Sevilla, you could go to Madrid and then take AVE train to Sevilla or fly to Madrid and then to Sevilla.