Best way to travel between Paris & Barcelona/Alicante

To me, the most "cost-effective" way is by discount carrier, as long as you're aware of luggage restrictions and extra fees. Vueling flies from CDG to Alicante and Barcelona...from Orly, easyjet flies to Barcelona, while Air Europa goes to Alicante. If you book far enough in advance, you can get a flight to Barcelona on vueling for 68 Euro (plus 6.50 Euro/bag) in mid-September....flight time is less than 2 hours. You can get a 29 Euro advance promo fare from Eurolines bus lines...but the trip takes 15 hours on an overnight run.

Here's a website for looking at discount airline schedules and fares: click here