Some expert says that the cost of a single F 35 is nearly an equivalent of two 4++ gen fighter Su 35. How did the Russians manage to built an exceptional aircraft which was relatively cheaper than its western adversary?

Firstly, the cost of the F-35 you see in the media is misleading. Today, it's price is comparable to a 4.5th generation fighter like the Typhoon or the Rafale. Lockheed-Martin is expecting the F-35 to cost less than a 4th generation fighter by 2019 at under $85 million with engine and full mission equipment. This isn't that much more than an Su-35 at around $60 million a pop and when you consider that the F-35 will eat the Su-35 and spit it out before it even knew was there, the price may actually seem too much for the Su-35. (I'm using hyperbole but that's not far from the truth. In BVR combat Su-35 is at a huge disadvantage. Within visual range however things are different. The F-35 is fat and lethargic compared to the purebred street fighter that is the Su-35, IF the Su-35 can get close.)

For comparison; a Eurofighter Typhoon costs around $130 million and India has recently bought Dassault Rafales at nearly $150 million each.

Secondly, the Russian fighters you see today are not “Russian” designs but “Soviet” designs. I know it looks like a small difference but it isn't.

This is important because the type of military equipment a country uses is decided by its military doctrine and the Soviets had a notorious lack of regard for the comfort and well being of her crews (in tanks, planes and ships, the Soviet designers always put crew comfort at or near the bottom of priorities. Simplicity, ruggedness and cheapness was the most important for the Soviet needs).

The Soviet Union was credited as being the second superpower in the world along with the US, but that wasn't really because of her economic might. Her military was huge, but that came at the expense of the people's standards of living.

So what was the Soviet Union’s doctrine then?

It might best be described with the words “human wave”. This was what shaped the military approach to how the Russians conducted their fights since really the beginning of the Soviet era. Imperial Russia used their superiority in manpower too, sure. But the increasing industrialisation in Europe dictated that throwing men at the problem became their de facto response to all threats soon after, because in the interwar the Soviet Union was sorely lacking behind in technology and industrial capacity.

The same goes for the Chinese as well. Some speculate that it's a mandate of the communist ideology, but it isn't. It's a mandate of huge populations combined with weak industrial capacity and poor infrastructure.

Soviet tanks and airplanes were riddled with defects and faults when they left their factories, but that wasn't a problem. The thinking was that it'd take them as far as it could and if it broke down they'd just leave it and get a new one. Strength in numbers was their mantra. Quantity rather than quality. It is said that Joseph Stalin himself uttered “quantity has a quality of its own”.

There's another reason why the Soviets preferred cheap, rugged builds to technologically advanced, but fragile builds and that is the Russian expanse itself. Russia is large. I mean VERY large. So it's not really developed in the infrastructure area. But the Soviets used this to their advantage. When the Germans attacked they simply kept retreating further and further into the Russian heartland while destroying everything they had to leave behind (scorched earth).

When the Cold War began in its earnest that poor infrastructure became an asset once again. The Soviets intentionally left their airfields and runways in derelict conditions. Because they were already designing aircraft to perform on poor infrastructure and if the NATO were to invade Russia, American planes wouldn't have been able to take off and land from these runways that were in poor condition.

So, the Soviet doctrine dictated that the military forces be vast in number and cheap to manufacture and replace and rugged to keep them running on Soviet infrastructure.

Epecifically for the air force, Soviet war planners had realised that the technological gap was too large to address. So they used their strength in numbers to counter their technological superiority. Numerous and cheap small fighters would overwhelm the advanced but limited numbers of American fighters, thereby gaining air superiority (same applied for the army as well).

Today's Russian designs like the Su-35, Mig-35 etc. are a transitional phase between that cheap and rugged approach and the more modern, technologically advanced approach the Russians are trying to apply.

You'll notice that those aircraft are all based on Soviet designs. The only truly new design the Russians have at the moment is the PAK-FA/T-50 and that one is not cheap.

With all that being said, it should be noted that the F-35 program is an anomaly. It's cost has been a surprise to everyone involved.

It was initially expected to cost around $200 billion, but major delays, redesigns and additional teething problems have nearly doubled that initial cost.

It's mostly understandable though. The F-35 is a true next-generation fighter and there are a lot of technological firsts. Those new technologies have teething problems as do all new technology. What's more the F-35 is trying to be (and apparently succeeding at being) 3 different aircraft at once, that's a really hard thing go pull off. F-111 tried that once and failed miserably as well as costing a lot of money.

In conclusion, current Russian fighters are cheaper than their Western counterparts, yes. But they are also less capable in current, high-tech skies and designed for a different war, one they are fast becoming obsolete for.