Itinerary for Budapest, Slovenia and Croatia--what makes sense?

You've allocated what I consider the bare minimum number of days at each destination. If you spend only three nights in Budapest, your first stop, that gives you just two full, (mostly) non-jetlagged days to see a city that a lot of us think of as a minimum-four-day destination.

Budapest-Ljubljana is something like 16 hours by train, so you'll need to fly. But there seem to be no non-stop flights, which means a time-consuming and comparatively costly travel leg. Go to skyscanner.com to check on what is available for your planned travel date. If you hope to see both Ljubljana and Bled, you'll need three nights there, because I suspect there won't be a lot of time left on your arrival day by the time you take two flights and get settled into your hotel.

Ljubljana is small and not so easy to get to (as per the above), but it is well connected to Zagreb (bus takes as little as 2 hr. 15 min.), which is a really nice city itself and a place where you could pick up a Croatian rental car to drive to Plitvice Lakes National Park. Obviously, if you travel from Ljubljana straight through to the park, stopping just long enough to pick up a rental car in Zagreb, it will be another rather long travel day. Your Plitvice visit may need to take place entirely on the following day, which will make you not early getting to your next stop (probably Split).

You haven't said how many total nights you are spending in Europe, so I don't know whether there's any flexibility here. I think you're going to feel quite rushed.

It's sort of a disjointed trip. Unfortunately Slovenia and Croatia are among the few Eastern European countries not well connected to Budapest, but I think there is an overnight train to Ljb. After that, a lot of long hauls on buses I suspect. Or hire a guide with a car.

Since you already have your flights, and if you arent married to Croatia and Slovenia, there are cheap direct flights from Budapest to Montenegro. The coast of Montenegro has a lot of the same flavor as Croatia, but less expensive, and the mountains inland are pretty special. Dubrovnik is just a short hop away by way of the Bay of Kotor which is really quite beautiful. Again, you will be on buses, or guide. The guides in Montenegro are pretty inexpensive though. Just a thought.

The problem with renting a car is the drop charge $$$$$$$

Fly to Budapest.

Train to Zagreb.

Rent a car and drive to Ljubljana and Bled. Be sure to buy a vignette driving pass for Slovenia at the border.

Drive back to Plitvice

Drive to Split

Drive to Montenegro (highly recommend at least a night there e.g. in Perast not just a day trip from Dubrovnik).

Drop the car when you get to Dubrovnik and stay in/near the old town (where you don't want/need a car anyway)

Fly home.

Forgot Korcula. You can get a car ferry there from Split (to Vela Luka, on the other side of the island from Korcula Town), and from Korcula town back to the mainland via a short very ride to Orebic. You could also just drop the car when you get to Split and take the passenger catamaran directly to Korcula town, then take a bus or catamaran down to Dubrovnik. But with four people, the economies of scale work out better with a car vs. catamarans and buses.

So, what have we figured out? Night train to Ljubljana, then rent a car and work south? The drop charge might be nothing in the same country or 500 euro. If you find out let us know. As for Perast, perfect, love Perast. With more time I would say Budva. Skip the town of Kotor as it's a disappointment after Dubrovnik. Even Dubrovnik was both fantastic and a disappointment at the same time for me. But worth the effort.

No way the drop charge would be 500 euros if rented in Zagreb (like I recommended) and dropped in Dubrovnik. In fact, it may be 0 euros. I've never paid a one-way drop fee within Croatia. You're more likely to see one for shorter rental periods.

I didn't get the sense that the OP has big time constraints, so I personally wouldn't recommend a night train to Ljubljana - I'd just take a day train to Zagreb.

I'm not a fan of night trains in general, but the choices here seem particularly unattractive (I looked at Monday departures):

Dep 5:40 PM, arr 5:57 AM. Transfer in Salzburg with nearly-three-hour layover (10:54 PM - 1:40 AM). Not sure what one might do in Ljubljana at that hour of the morning.

Dep 6:40 PM, arr 5:57 AM. Two transfers, one of them in Villach at 3:57 AM. Again a super-early arrival.

The following are overnight routings but not night trains in that there are no sleeping accommodations:

Dep 7:10 PM, arr 10:18 AM. Six transfers, one involving a 3.5-hour layover beginning at 12:44 AM.

Dep 11:20 PM, arr 2:14 PM. Two transfers (both with layover of at least 1.5 hours).

12:20 AM, arr 2:14 PM. Four transfers. One of the transfers involves an almost-three-hour layover beginning at 1:13 AM.

What a lousy introduction to a fabulous city. I think few travelers who took any of those trains to Ljubljana would be in condition to enjoy the city on their arrival day.

Edited to add: The above information was taken from the Deutsche Bahn website. Perhaps there are additional options not shown there, but I've generally found it comprehensive.

Thank you to all for the great advice. I'm thinking a train or flight from Budapest to Zagreb, rent a car and drive to Ljubljana for a couple of nights, day trip or overnight to Lake Bled, drive to Plitvice and stay one night. After that I'm still a little stumped. Will drive south and end up in Dubrovnik of course. But where else to stay? I don't really want this to be an all city trip--would love a couple of nights in a smaller town. Even the islands, as a stayover, are not a must. I like the idea of driving into Montenegro and staying in Perast--will look into that.

One nice thing about the Balkans is that there aren't many huge cities. Zagreb is probably the biggest of all of the places you will go. Ljubljana feels like a big town more than the capital city of a country. It's not like Budapest (which is enormous), London, Paris, etc.

Split is not tiny either but doesn't feel that big, at least in the part you would probably visit.

But if you want smaller towns in Croatia? Try Sibenik, a lovely town on the coast north of Split. Trogir is really close to Split - much smaller and more intimate (and charming) than Split but more touristy (it's another "old walled city") and a little less interesting. If you want to see another national park, try Krka (near Sibenik).

In Slovenia, I highly recommend Ljubljana itself, but if you like small towns there are some nice ones nearby. The town of Skofja Loka is lovely. It makes a scenic detour (worth a stop, even if not overnight) on the drive from Ljubljana to Lake Bled. The drive from Skofja Loka to Bled via the mountains through, Jamnik and Kropa (not via the highway through Kranj) is really beautiful and scenic. Before you get to Bled, you'll get to another nice old town, Radovljica (mentioned in Rick Steves's book), which is a more charming alternative for overnighting near Lake Bled - nothing wrong with the town of Bled itself, which is very convenient for a stay, but it's a bit touristy and not especially charming.

Using rome2rio, I see that there is a shuttle for B-P to Ljub, which is quicker and not much more expensive than a bus. Within Croatia, I like Flixbus.

Thank you so much Andrew H--great suggestions! A couple of those small towns seem like just what I'm looking for!