1. Thus far the Erieye ER has only been qualified on the Bombardier Global 6000, not the Saab 2000. If the PAF were to select the Erieye ER - with integration to the Saab 2000 - it'd likely have to pay the extra cost of doing so (i.e. integration work, tests, certification, etc).
2. The Erieye ER would be costlier - it necessitates new support infrastructure. The UAE paid $238 m for each Erieye ER, while the PAF got the additional three Erieye for around $130 m each (thanks to the fact that it already has the training, logistics and maintenance infrastructure already in place for the Erieye).
3. Prior to the 2005 Earthquake, the PAF had intended to build a fleet of 6 Saab 2000 Erieye AEW&C.