How would you say will be best for us to go from Seville to Lisbon. Airfares are out of question!

Thanks

Actually, they are having some promotional rates on airfares -- so don't count air travel out completely. e.g. EUR 99 to go to Rome, Paris etc.
At least check on www.iberia.es.
Normally air travel Sevilla -> Lisboa would route you through either Barcelona or Madrid and run you probably 350 Euros.
But maybe someone is having a sale.

Anyway, by road it's about 5 hours (400 kms).

Train: Take the AVE up to Madrid... EUR 65 and then the night train to Lisbon. EUR 120 (per person) for shared room or 200 for your own sleeping cabin; 240 for 'Gran Clas' and well worth it.
Rates are at: http://www.renfe.es/viajes/precios_int.html#opcion1

If you're coming from outside Europe and get a EurRailPass, in advance, the prices could be much lower (e.g 120 per person for Gran Clas).
See http://www.renfe.es

I hope this post is not too late to be of some use....
I recently had to make this same decision. I determined that the best way, in terms of time and money, was to take a bus from Seville to Lisbon. You can get a bus schedule from the local tourist offices. Direct buses operate every day of the week; some days there are two buses, other days just one. The schedule varies by day of the week, but every day there is a direct bus at 11:00 AM operated by the Anabal bus line. At least, this was the schedule in October.

The published time to Lisbon is 4.5 hours and costs 50 euros. IMPORTANT: in spite of what locals may tell you about not needing a reservation, be sure to either make a reservation or better yet, buy a ticket in advance. This is not an easy task. I learned this the hard way. It takes perserverance on your part. The long-distance bus system is somewhat chaotic, disorganized and generally not user friendly as far as buying a ticket in advance. The bus ride itself is great - roomy, comfortable seats.

Alternately, you can take a connecting bus service rather than the direct service. In this case, the journey is longer, maybe 7-8 hours. You would most likely travel to Badajoz, Spain and then buy another ticket from Badajoz to Lisbon. The total cost is around 25 euros. This is what I ended up doing because the direct bus was sold-out the day I wanted to travel.
Good Luck.

There's a Viajes Julia (DBA Eurolines) bus about 4-days a week. It departs Sevilla's Plaza de Armas bus station at 15:00 (ET) and arrives in Lisbon (Oriente) at 20:45 (PT) and at Lisbon's main bus terminal on Joao Crisostomo at 21:00 (PT). That's 7-hours: Check it out at http://www.eurolines.es/Portugal.htm

We made our reservations on line and bought our tickets at Plaza de Armas about 2-hours prior to departure.