Iranian top brass has been well aware of where their budget would get the biggest bang in defence of Iran. With the technology at hand and the current sanctions, it would be a waste of money to invest in any new designed aircraft.
Iran's adversaries have the best air forces known to history and nothing Iran could produce that would help Iran's military capability in the air. It has been very wise for Iran to divert attention to where its adversary can be vulnerable. That is why a good portion of Iranian military budget has been allocated missiles and air defence.
Manufacturing a new jet fighter is very expensive and in the end it will not give much leverage to Iranian military. A jet fighter is designed to perform something like 30 years of service. Iran needs access to better powerplants and an up to date radar not to mention other avionics, weaponry and a new carbon fiber material.
Some of these technologies have been available already more or less but the radar and a suitable powerplant have not been available.
However, with the past two weeks events which let to capture of the latest US air force technology things could be very different. The two most important technologies now in the hands of Iranians are the stealth technology and the top of the line AESA radar. These are the two technologies that have made F-22 and B-2 to be the master of skies.
If Iran could reverse engineer the technologies at its disposal, then the military strategy of Iran will definitely change so much that budgets for such endeavors do not seem a waste any longer.
Stay tuned!
Catsoo