If you can avoid using BA, you can avoid significant surcharges using AA miles. AA itself has no charges beyond government fees. The same is true of AB, though award flights on AB have recently become impossible to book far in advance. IB has lower surcharges on award flights via MAD, but award flights on IB cannot be booked online; a phone call to all is required.

Budapest and Bratislava can easily be visited from Vienna by train. An open-jaw flight returning from Munich should also be possible to arrange, though in all these cases you and your friend would be responsible for the train transportation..