Cheapest private lessons in Europe?

When I started I watched couples that took only classes for a few years. A nice leisure activity, more expensive than milongas, but most of that students didn't really learn to dance.
I don't understand why people take classes as couples, especially classes with 10-20 students.

I know that many people choose classes by checking prices. The cheapest classes are usually the biggest.
They can pay $5-10 more for group classes and get more attention in semi-private environments by dancing more with teachers, not their partners.

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