I was actually thinking of the Viajes Julia (Eurolines) bus (9.5 hours Sevilla-Lisboa). I took one of those 2-years ago. It's a real drag, but it gets you there. Unfortunately, in the off season it only runs about 3-days a week, so you'd have to schedule yourself accordingly.
I don't do railpasses, especially in Portugal where rail travel is cheaper than just about any-where else in Europe. Alternatively, you could bus from Sevilla to the Algarve (Faro or Lagos) and catch a train from either of those places to Lisboa. Check
http://www.cp.pt (Caminhos Portugueses) for schedules.
For a centrally located, inexpensive place to stay in Lisboa e-mail my friend Carlos Ferreira: restrela@esoterica.pt