For a very long time now, a military aircraft is not a mode of trasportation, it is a weapons platform.
If all you want is a fuselage, wings, and an engine, you can build an aircraft for $10 million.
However, if you want a fully integrated avionics package including a decent radar, navigation, smart bombs, targeting pods, electronic countermeasures, failure redundancy, computer controlled flight controls, electronic full authority digital engine control, etc., it will cost $50-60 million.
The cost of an aircraft is not just how much the steel, titanium, aluminum, and paint cost, but also how much it cost to design and develop the airframe. When you rip off someone else’s design, you bypass a large hunk of that cost.
You also need to take into account the deep corruption within the Russian Army and Russian Military Industrial Complex.