Fly out of Ljubljana or ?

Two one-way tickets are always A LOT more expensive than buying a multi-city (open jaw) ticket. A multi-city ticket is one transaction, one full trip. For example, I just bought a ticket from Priceline going from Vienna to Newark then Greensboro to Vienna. It was one ticket, one payment, one transaction. Much cheaper this way than buying two one ways - probably about $1,000 cheaper.

For your trip, it doesn't make sense to take a 6-7 hour train ride to Vienna at all. Just fly out of Ljubljana to a major airport in Europe which has connection to Portland. I use kayak.com for all my travel searches.

The airport near Ljubljana is fine, and we flew out from it once. An open jaw ticket...into Paris and out of Ljubljana is fine and a quick search at Matrix Airfare website found very attractive fares for some random dates in September. Oh, I price compared two one-way tickets versus an open jaw itinerary and the cost was about 15% more for the two tickets versus the open jaw tickets. For flights within Europe, I use the Skyscanner website.

Another possibility would be flying home from Zagreb, which I think has more flights than Ljubljana. As I recall, the two cities are only about 2 hours apart by train or bus. For Portland you might do equally well from Ljubljana, but it's worth checking.

It appears that your tour doesn't get to Zagreb. To me, it's definitely worth a full day at the end of your trip.

We have done this tour and also the Best of the Adriatic. We flew out of Ljubljana following the Eastern Europe Tour and into Ljubljana to start the Adriatic Tour. it is a small, easy to navigate airport and a short drive from Lake Bled. Our tour guide arranged transportation to the airport for all who wanted it. We flew from there to Boston through Munich. We have done a number of RS tours and as mentioned, we have always booked our trips "open jawed" as one continuous booking regardless of the number of stops.

Definitely open jaw "multi-city" (same thing) if at all possible. Fly into Paris, fly home out of say Venice, Zagreb, etc. You can try Ljubljana but I am guessing you won't find a good flight with only one connection back to PDX. I always shoot for the Delta direct flight from Amsterdam to PDX that leaves about 10am, so try to connect to that - or the Condor flights (not every day, not all year) from Frankfurt to PDX.

The Delta Amsterdam flight probably leaves too early to make a connection from say Venice on the same day reasonable; you could try a shuttle service like GoOpti to get you to Venice in time for the early flight, but that would mean leaving Ljubljana crazy early, most likely. If the Condor flight from Frankfurt is available on the day you want to fly, I think it leaves later in the day so a connection from Venice or Zagreb might work on the same day.

Of course, you could just stage a final night or two in say Amsterdam or Frankfurt to make flying home the next day super easy. In that case, in addition to the open jaw ticket to/from Europe, book a single one-way flight separately within Europe. That's what I've done more than once, but it does eat up more time away from home, and not everyone has the time. Adria is the Slovenian national airline (I think) that has direct flights from Ljubljana to many European capitals, but other airlines may have direct flights to Amsterdam and Frankfurt too. Venice (get to it via GoOpti or DRD) or Zagreb (GoOpti or by bus/train) might be cheaper or have better times. Check all the options with Google Flights or Skyscanner.

I agree with everything Don has said as I have done exactly the same thing-into Ljubljana for one tour and out of Ljubljana couple years later when leaving the EE tour. It's a very easy airport to navigate, not crowded and the folks there are helpful and pleasant. We had stayed in Ljubljana for several days before returning home (last August) but it's correct that your guide will help you arrange transportation to anywhere you are going before the end of the tour. I guess it depends on what you want to do when your EE tour is over. Our trip home involved a flight to Munich from Ljubljana and then home to Denver from Munich. All went smooth as silk; we flew Lufthansa for all flights. I would recommend you book multi-city/open jaw where ever you decide to fly home from.

There is just no easy way to get back to Portland from Slovenia. You could possibly take EasyJet to Gatwick and catch a bus over to Heathrow for a seasonal nonstop Delta flight into Portland.

Really depends when you go - even which day of the week not just what season.

I checked a random date in May (May 8). There's a pretty good flight connection: LJU-FRA (Adria) and FRA to PDX (Condor) with a 5:40 layover - plenty of time to make what should be an easy connection.

I agree with the posters who suggested extending the trip so you don't have to fly back to the US in one day. For example, fly from Ljubljana at a civilized hour to a larger city and stay overnight there before flying back to Portland. Having to leave early going home sort of ruins the tail end of the vacation, in my opinion.