travel by car between countries

Thank you. That's what my research showed too. I guess we will fly. Trains take way too long and are costly as well.

Sure, its only 1000 miles.

Yes, but it's over 1,800 kilometres. In theory (according to the Google Maps journey planner) that's 16 hours of driving. See many other threads on this forum about taking hire cars from one country to another (short version: it's really expensive). Vueling, Air Berlin and the Austrian airline Niki all fly direct from Vienna to Barcelona. It takes 2 hours 15 minutes flying time. By train you could go Vienna - Zurich - Paris, then get the sleeper train to Girona over night, then Girona to Barcelona is only 40 minutes on a Spanish AVE high speed train. Door to door travelling time around 24 hours.

Not what you asked and presuming we are talking rental car - will you be happy with the extraordinary (to me) drop off/repatriation fee?

I don't know what the extraordinary repatriation thing is.

Pick up a rental car in a country (say...Austria) drop it off in a different country (say...Spain). Might be convenient for you, but you'll get hit with a BIG drop-off fee because you didn't return it to the same country where you rented it. It can be an astronomical fee: hundreds and hundreds of Euros. Return your car to the same country where you rented it = no drop off fee.

I just have one word for you: Vueling. They're a Spanish airline, and they have many, many destinations to/from all over Europe. And they're a budget air carrier flying to Barcelona from Vienna. Many who used to use trains find it quicker to use airlines like them, and it's a big savings on time and ultimately money.
Distances to and from Spain are sometimes deceiving, as it's a pretty large country.