score:6
Germany doesn't seem to impose a vignette on tourists. Hungary - for minibus it's about 22β¬ for a week. Both Slovakia and Czech Republic will require about 12β¬ for a 10-day vignette. Serbia requires about 5-6β¬ 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.