me and my sis are trying to plan a road trip from Sofia, Bulgaria to Berlin, Germany. My question is does anyone know what are the road taxes at Serbia, Hungary, Slovakia, Czech republic and Germany for a car/mini bus(up to 9 people)?
Germany doesn't seem to impose a vignette on tourists. Hungary - for minibus it's about 22€ for a week. Both Slovakia and Czech Republic will require about 12€ for a 10-day vignette. Serbia requires about 5-6€ per 100km, depending on the route - so, you'll need to calculate it for yourself.
Hope that helps.
P.S. Eurovignettes.eu might be of use.