Train From Barcelona to Lisbon?

Not at all. the bus probably is cheapest but that ride to me would be pure misery because how long it would take.

Don’t even think about it. It’s a very long ride on the train with a connection and intolerably long by bus. The route is well served by regional airlines.

Portugal and Spain (even western Spain, never mind Barcelona which is practically in France/Italy) are not well connected by rail. Unless you have unlimited time and don't care how long it takes or how miserable you would be upon arrival, I think it would be crazy to go from Barcelona to Lisbon by train (or bus).

Find a cheap flight. It won't cost much more and you'll get there in a few hours rather than forever-and-a-day.

I would definitely consider flying from Barcelona to Lisbon. Economical and easy. A couple years ago we flew from Porto to Madrid on TAP Airlines. That route was only €38. Well worth it especially if you purchase your tickets in advance. We did take the train from Madrid to Barcelona. That was quick and inexpensive.

There is only 1 mode to consider.
Flying.
Both Vueling and TAP have one-way fares under $60 USD.

Barcelona to Madrid ... train GOOD.
Madrid to Lisbon ... train NOT GOOD.

It's 1200 kilometers from Barcelona to Lisbon. Net driving time per google maps is 12 hours.

Cheapest is probably flying on Vueling or TAP.... 50-80€ on average and a couple of hours flight....

Barcelona to Lisbon from €78

https://www.seat61.com/international-trains/trains-from-Madrid.htm#Spain-Portugal

I researched this and decided to get a flight on TAP. Based on the reviews of the train and the time, I expect it will be the best bet. The flight is short and cheap!