You might consider routing your train travel through Croatia when traveling from Budapest to Slovenia. We traveled from Ljubljana down the Sava River to Zagreb for a couple of days before continuing on to Budapest.We found Zagreb to be a very interesting city and were very pleased with our stay there. It was inexpensive, like Slovenia, and historically a very interesting city due to its geographical location and the various waves of empire that have washed over it, i.e. Austro-Hungarian, Ottoman, and, of course, the Soviet-backed Yugoslavia.

You might even consider visiting the the Croatian Adriatic coast.

John in San Diego