The vignettes are ONLY for motorways. If you don't plan to use Austrian motorways, you don't need a vignette. Additional charges are only incurred on a few mountain passes and tunnels. You can buy vignettes at the border or at most offices of various automobile clubs on the way. The charge is 7.70 Euros for 10 days or 22.20 Euros for two months. Unlike Switzerland, you don't need a separate vignette for the caravan, too.