There is wireless shop at arrival hall at Vienna airport near OBB/CAT train access. The shop didn't have/sell 3 SIM card but sells T-Mobile and Orange (?) SIM cards. I bought a T-Mobile SmartKlax prepaid plan for 15 euro with 2000 minutes / 1000 sms / 2GB data and it was activated at the store.

It may not be least expensive but I didn't have to look for a other options on weekends.