The fastest trains from Paris to Toulouse are around five and a half hours. You can book at www.capitainetrain.com, with the cheapest fares available about three months before the journey time (so you won't find anything for next summer now).
Alternatively, both Air France and Easyjet offer flights from Paris to Toulouse, but when comparing the times, remember to include the journeys between city centres and airports and the time spent in security queues and departure lounges.
You don't say if you are staying in Paris beforehand. If you are flying into Paris from elsewhere and want to go straight to Toulouse, a connecting flight from the same airport will be easier than the train.