Vienna to Barcelona

Go to Bratislava/Vienna and take Ryan air. Ryan air goes to Barcelona Girona

You should as well check Flyniki. Maybe they are a little more expansive than Ryanair. But you can fly from Vienna Airport to Barcelona Airport instead of Bratislava to Girona. This will save you a lot of time and maybe the complete travel price (including ground transportation) will turn out cheaper than Ryanair

Good point made by #2. With Ryanair always calculate the total fare from city center to city center, don't base your decision solely on the airfare.
Flying is the only feasible option. Eurolines busses don't operate on this route and the train takes over 26 hours with at least 3 or 4 changes enroute.

try Vueling.com

Vueling is a spanish air carrier, another cheap carrier like Ryan Air. i flew in and out of barcelona with Vueling a few times.

There are flights from Barcelona to Wien

Thanks for your help guys. Much appreciated.