From Trieste to Croatian Istria you cross Slovenia in under an hour. Slovenian off-motorway prices are regulated and lower than Italian prices. Refuel in Divača, Sežana or Koper before continuing towards Dragonja.
Yes. Italian prices are among the highest in Europe, and regulated Slovenian off-motorway prices are usually below Croatian prices too.
Yes, for motorways and expressways. If you only use regional roads towards Dragonja, no vignette is needed.
Around Koper and Lucija — the last regulated prices before the Dragonja border crossing.