The issue is with the iranian budget, they can't spend everything on expensive imported arms. At least not if they want to fight and win.
Right now - Iran cannot fight as it does not an an airforce worthy of the name. Withought having an airforce to compliment its SAM systems, Iran will lose control of its airspace very quickly. SAM systems and aircraft compliment each other and protect each other to enforce control over a given space.
Even though Ukraine itself isn't doing well, the Ukraine formula of using a lot of inexpensive hand me down arms should probably be considered one of the most optimal method.
Ukraine has understood the need to be able to protect its airspace hence has been asking for, and recieved F16s and Mirages 2000s, all of which are BVR capable platforms.
Payment to China is the least of Iran's worries, they have a lot of funds or other things to pay with.
If they cannot effectively protect their airspace, then anything else they would buy is not going to be effective. It will be destroyed on the ground.
The issue is the running costs of some expensive foreign fighters, buying replacement parts that can't be made in Iran, having no ToT and so on. Not to mention J-10 with smaller combat radius will have to be bought in larger numbers due to Iran size.
Iran has been tinkering with attempts at home grown solutions, and none of them have been able to yield a viable and effective platform. There comes a point where there is a cross over between having "actual" military capability and tinkering. If Iran was capable to build an effective platform, it would have done so by now. What Iran needs urgently is an emergency level of infusion into its airspace given all the new military threats it is facing, including recurring direct attacks by Israel. Israel will work out how to destroy Irans IADS shield, all IADs systems are vulnerable if they dont have an airforce to cover for them - they compliment each other to form an effective shield.
Let's face it, J-10 (and similar contemporary like Rafale or Typhoon) are heavily built to awe in shows and peacetime, but do not excel in peer conflicts, unless you can field a shit ton of them. Their asset to China is actually their low price compared to twin engine fighters, which isn't an asset for import buyers, as the J-10s get marked up a lot.
Crazy statement - wont bother replying to this...