I believe that 'the less, the better' suits a 16-17 day tour more. The less locations, the more you can stay in each one, hence you get to know the people/the culture/the food better. The memories on that town/city stay longer, and you don't lose the impression of the place you've visited as well.
I think that more than 4-5 locations per one trip is worthless. Firstly, you're spending way too much money on transport (I know you stated you wanted the tour not to be expensive, but with around 10 locations in mind, it's quite impossible). Secondly, all you're pretty much doing is rushing from one place to another, from one bus/plane to another, and you're missing out on the potential experience you could've had. Thirdly, you can always say to someone 'Oh yeah I've been to [insert location here]', but you won't actually remember anything, but a few sights, some local sandwich you had and that's it.
Before I start, I should mention that I've sort of neglected the money issue, but I've still included all the prices. (I'm taking this way too seriously, this is a game for crying out loud). I have also made this itinerary in a way where not all of the places are on the coast/in the mountains/near a river/lake. I've given you the best of both worlds, or I guess three worlds, in this case.
With that being said, I'm gonna give you my short list of amazing locations (I haven't picked any dutch cities/towns as you live there, so chances are you've probably seen most of them):
Amsterdam, The Netherlands(taking it as a point of departure)
Ljubljana, Slovenia (flight is average 300 euros at this time of the year)
Bled, Slovenia (a one-way bus from Ljubljana to Bled is not even over 10 euros, so assume a two-way is around 15)
Rijeka, Croatia (transport from Ljubljana to Rijeka shouldn't be over 15 euros)
Karlovac, Croatia (Rijeka - Karlovac transport isn't over 15 euros)
Zagreb, Croatia (bus from Karlovac shouldn't even be 10 euros)
Back to Amsterdam (flight from Zagreb is around 170, 180 euros)
Total for all means of transport - ~525 euros (not by any means 100% accurate)
Lenght of stay in each town:
Ljubljana - 21st to 24th
Bled - 24th to 28th
Rijeka - 28th to 1st
Karlovac - 1st to 4th
Zagreb - 4th to 8th
Accommodation prices in each location (these are hostels, because they are cheaper than apartments):
Ljubljana - ~50 euros for 3 nights
Bled - ~100 euros for 4 nights (a bit more expensive yeah, but Bled is so worth it)
Rijeka - 50-60 euros for 4 nights
Karlovac - 40-50 euros for 3 nights
Zagreb - 40-50 euros for 4 nights
Total price for accommodation: ~300 euros
Now, some info on all of these towns:
Ljubljana - capital of Slovenia, you're basically walking into the Slovenian centre of everything - economy, culture, education etc. Being the largest city in the whole country, you can expect to see and do a lot of things. Apart from all the antique buildings and churches to see, visit the Triple Bridge - 3 bridges collapsing to make one. It's delightful to walk over and offers an amazing view! Visit the many squares (such as Prešeren Square - central square), alongside of Tivoli Park, as well as take boat tours, to view the city from another perspective. As for the food, you can buy it in the grocery stores or supermarkets, or feel free to be another one of many people who buy their street food - it's hella good.
Bled - Bled is quite small, but it's one of the most popular tourist attractions in Slovenia (you can already tell that by the accommodation price). Why? It's the Lake Bled that makes it such a popular tourist attraction. Not only does the lake offer the ability to swim during summer, it offers a breathtaking view literally from everywhere! The island in the middle of it just makes it so much more satisfying to look at and enjoy. Have a walk around the lake, visit the Bled Castle, and try the most amazing vanilla and cream pastry ever (the Bled Cremeschnitte).
Rijeka - a coastal town near Slovenia, it's the third largest city in Croatia. Being so large and a popular attraction, it's not too expensive - only 50-60 euros for 4 nights in a hostel. It offers a lovely view towards the Adriatic Sea, and every day you can be amazed at the size of ships that come in the local port (which is the largest Croatian port). Visit the Torpedo Factory, antique cathedrals and swim at one of many beautiful beaches along the coast of Rijeka.
Karlovac - Moving away from all the waters (there's still a river going through Karlovac, but at least there's no seas or lakes) we're coming into the mountain town of Karlovac. Small, but offers plenty of things to do: visiting the Museum of Army Collections from the Croatian Homeland War, rafting tours, bike tours, boat tours, going to the town square, you name it.
Zagreb - We're coming to the end of our trip, and we're setting foot in the biggest, and capital city of Croatia. You'd expect the accommodation to be way more expensive, considering. You can take the Plitvice Lakes day trip from Zagreb, but before that, be sure to visit the Maksimir Park and the Zrinjevac Park - they are both wonderful to relax in. Go to the local zoo, and after a tiring day, eat at Sofra - a restaurant with Bosnian specials.
EDIT: Taking into account the accommodation & the transport prices, as well as the money you spend on your own, I assume, for this kind of tour, you'd need 1500 euros (complete estimate).
Now, regarding the question: Why should I go here?
I've kinda answered that in the small description I left for these locations, but I'll add another thing: the Balkan countries are sometimes left out as an option for a vacation/tour/trip, as people's general attitude is 'OOOOOOOOOOOOOOH PARIS OUI OUI OMELETTE BAGUETTE' and 'OOOOOOOOOH JA GERMANY IST BEST MMM WURST UND BEER JAAAAAAAAA' so they usually visit those countries, but there's no reason to leave these out, as all of Balkan is amazing, pretty much wherever you go.
P.S. Please forgive me if I've made any grammar mistakes.
If you are reading this bit here, that means you've come to the end. I at least fucking deserve a like after everything I've written.
