How much did the 18 F-16, the 2nd hand RJAF F-16s and the MLU of our existing fleet cost us each? Once you have those numbers, how much does a new J-10B/C costs? Then we can do the comparison to see whether what PAF did made sense or not.
Lemme jog your memory back to 2005, when it first came out that Pakistan Air Force was going for Block-52 F-16s. How many Block-52s was Pakistan Air Force planning on getting? It was announced that Pakistan Air Force was going to order 75 Block-52s. You think Pakistan had the economic clout to go for that many Block-52s? The answer is NO! American military aid was going to subsidize the sale. After the Earthquake however, Pakistan reduce the order to just 18 Block-52s. The same way Pakistan was going to buy the 8 Block-52s from the US, before Trump decided to cut off American Military Aid to Pakistan, which was going allow Pakistan Air Force to get the 8 Block-52s at half price. After the Aid was cut off, Pakistan cancelled the planned acquisition of 8 Block-52s.
Pakistan also signed a deal with China for 8 brand new S-20 submarines, plus 4 brand new Type-054 frigates. You think Pakistan had the money for those purchases? The biggest military acquisition in the history of Sino-Pakistan Alliance, worth billions of dollars. Pakistan had no money for 8 new submarines nor the 4 new frigates. The only reason why Pakistan can afford to go for that many subs and frigates is due its strategic alliance with China. The same way Block-52s resulted due Pakistan's strategic partnership with America in the war on terror.
Countries like Pakistan rely on other methods for defense acquisitions, not everyone can just throw many at things like the Saudis, Qataris, Emiratis or Indians do. Indonesia used barter trade for its Flankers, with Russia. So this whole run around about costs, is in effect, irrelevant. Since China is Pakistan's primary ally, it's not a matter of how much money is needed for a fighter acquisition. Rather it is about the strategic planning, the absorption of technology, the capacity of the Pakistan Air Force to maintain an absorption rate of new ToT, while also have enough expertise manpower to cater it.
At present, there are some options which Pakistan Air Force may go for:
1. Buy J-10Cs in small batches to go upto 80-90 or more fighters, until the 5th Gen Stealth Fighters are inducted. Along with additional Vipers to raise the fleet size to 100 fighters. With 250 Thunders as over all production.
2. Buy more used F-16s, increasing the fleet size b/w 100-150 Vipers, and continue production of PAC to 300 Thunders. Not buying J-10Cs and waiting for Stealth Fighter to become available.
3. Keep current force projections to 200 Thunders, 76 Vipers (+15 Jordanian F-16s) and keep Mirages going for as long as possible.
4. Breakthrough in deal with Russia, buying Su-35s in batches over the course of the next decade. Replacing Mirages and F-7s. Stealth fighter would replace Vipers.
The most likely scenario from the four stated above would be Pakistan Air Force having a mix of J-10Cs, JF-17s & F-16s, consequently phasing out the oldest Mirages and F-7s. If budgetary limits are expanded based on Chinese military aid program, then it is likely that Pakistan Air Force would try and get ToT for J-10Cs.
I would say let's see what happens once the Block-llls are rolled out. Will have better idea then.