Well, both cost roughly the same: 90 million per unit.
Just to put some perspective on it:
A spitfire cost: 1 million (costs updated)
An F-16 cost: 18 million
A MiG 35 costs: 40 million (2007)
How good are these planes?
Are they worth the money? Well, according to a recent report the F-35 engine is described as a blowtorch surrounded by fuel: they keep catching fire.
What’s your opinions on this sort of investment?
I write as a historian of aviation (in part) and someone with substantial knowledge
of aeronautical engineering and the international arms trade.
There has been a vast (exponential) increase in state-of-the-art aircraft complexity
since the 1930s, when the Supermarine Spitfire was designed by a small team of engineers,
led by (the dying) R. J. Mitchell. Modern design teams are much much larger
(requiring much more pay), including in specialists in avionics, radar, and other
fields that hardly existed when the Spitfire was designed.
And the modern research and development cycle is much longer and more costly.
In late 1944, the Heinkel He-162 (an early jet fighter) went from its first sketches
on the drawing board to its first flight test in only about 90 days. (Working around
the clock, some German engineers slept on cots in the workplace in order not to
lose any time traveling back and forth from their homes.)
In the early 1980s, India (HAL) proclaimed that it would develop a world-class LCA
(light combat aircraft) with supposedly indigenous air frame, engine, and radar.
That project was wildly overambitious. India eventually had to import almost all
the technology. The aircraft was not introduced into service until 2015 (!). when
it already was obsolete.
Many ignorant Westeners still seem to assume that the (former) MiG (later
known as Mikoyan) OKB still produces most of Russia's leading fighter aircraft.
The MiG-29 (designed in the 1970s, introduced in the early 1980s) was the last
MiG to be a major fighter aircraft used by the USSR or Russia. For the past few
decades, Sukhoi (not Mikoyan) has dominated Russian fighter aircraft design.
Russia does plan to buy some MiG-35s, largely to increase its appeal in the export market.
But Sukhoi fighters (Su-27, Su-30, Su-33, Su-35) are the backbone of Russian fighter aviation.
The most advanced Russian fighter under development is the Sukhoi Su-57.
Not many countries can afford (even if the USA were willing to export it) the F-35.
So there's a major market for more affordable aircraft that are less than state-of-the-art.
After the USA reneged on an agreement to sell some F-16s to Pakistan (which already
had paid for them--Pakistan eventually got a partial refund for non-delivery),
Pakistan paid 500 million USD (a comparative bargain) to China in order to develop
a fairly modern fighter aircraft according to Pakistani specifications, which would
be built in a factory (set by the Chinese) in Pakistan. Reportedly, Pakistan has been
very satisfied with the JF-17 Thunder, which supposedly can compete with all
except the most advanced Indian fighters (such as the French Dassault Rafale).
Recently, China sold several advanced jet trainers (based upon the MiG-21 but with
more modern avionics) to Sudan (a very poor country), a market that probably
would be ignored by the merchants of more advanced and expensive aircraft.
If I were a minister of defense and asked for my advice on procuring combat aircraft,
I would say that it would depend upon my country's financial resources, general
level of technology, and strategic situation (in terms of likely threats).
Iran's air force still chiefly depends upon (1970s American) aircraft inherited from the Shah.
Western countries would not export any advanced combat aircraft to Iran.
So I would suggest that Iran consider, on the high end, the Russian Sukhoi Su-35,
or, on the low end, the Chinese JF-17 Thunder. as upgrades.