I've seen the FlixBus, and City2City, and MeinFernBus in Germany that travel between German cities and beyond for very reasonable prices - like 8 Euros from Munchen to Frankfurt. Is there a bus service like that in Spain that we can use to get from Barcelona to Toulouse or really, anywhere in the south of France?
There are many bus companies within Spain, but for international trips, start with www.eurolines.com. The fastest trains from Barcelona to Toulouse take about 4 hours with a connection at Narbonne, or one afternoon departure is faster and direct. Train tickets are cheaper when you buy them early, up to 4 months in advance.