Not sure what you have to work with. Are you brooding inside of a building or do you need something that will stand up to the weather? What kind of temperatures are you facing? I can't imagine brooding 50 chicks inside of your house but is it a climate controlled area? I brood outside in the coop, the temperature swings are my biggest challenge.
It's hard making suggestions without knowing what you have to work with. I can't see the opportunities being any different in Montenegro than in the US or anywhere else. The principles will be the same. You want something that provides predator protection and protection from the environment. If that is inside a building that can be easy. Some people get large cardboard boxes from an appliance store and tape them together for a nice large brooder. If it needs to grow just tape in another box. If it is exposed to the weather or predators it's a different issue.
You need to provide an area warm enough in the coolest conditions and an area cool enough in the warmest conditions. As long as they have the option I find my chicks straight from the incubator can manage that themselves.
You need access to it for daily maintenance, feeding, watering, and cleaning. How large it needs to be depends on how old the chicks are when you take them out. You need to be able to keep it dry. A wet brooder is a dangerous brooder.
It sounds like you are hatching several times a year so you might want something permanent. I appreciate you being on a limited budget. There is nothing wrong with reusing and recycling things. The chicks don't care what it looks like as long as it is functional. Sometimes people do. I do believe in building for your convenience, no need to make it harder to manage than you have to.
Some ideas for inexpensive materials. Do you have a social media program similar to out Craigslist where people in your area can list things for sale or maybe for free. Sometimes you can find a building for free if you will relocate it. Often you can find material for free.
Ask at construction sites for excess materials. Sometimes they use stuff as installation aids, maybe temporary supports or wood used to frame a concrete pour. When they finish with them they have to dispose of them. Here that could mean paying extra money to dispose of them as trash so they are happy to give them away.
I'll include a photo of my brooder permanently built into the coop. It's about 1 meter x 2 meters and will hold about 25 chicks until they are 5 weeks old.
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Not sure if any of this helps or not. Good luck!
