Comparing specifications of Cheetah with Mirage V, Mirage V has greater ferry and combat range, higher service ceiling and can carry same weight of payload ie 4000 kg.
If PAF wanted to have Cheetah option, they would have opted for it.
MRF and PAC have the capability to manufacture complete airframe structure of Mirage aircraft.
However, manufacturing a new airframe structure along with other parts such as landing gears is very costly as compared to extensive overhauling of older airframes. During the overhaul complete bulkhead of Mirage is being inspected for any anomaly, all damaged bulkheads parts and critical load bearing members are being replaced with new ones, complete aircraft rewiring is being done and its engine, other parts and equipment are being overhauled. In short Mirages coming out of MRF have their service life extended.
In my opinion investing on Cheetah option would have been wastage of scarce financial resources. PAF opting to buy phase out Mirage fleets from various Air Forces is a cheaper solution as it serves the purpose to build enough fleet after extensive overhaul, upgradations and modifications.
You may have your opinion on the subject, but PAF leadership take decisions according to their strategic requirement with optimum use financial resources.