For that you need EW systems, like ASELSAN KORAL, that can deceive the enemy to detect phantom images to render complete delusion to both man and machine..
For every disease there's a cure as per our belief system. S-400 is no exception as humbly shown by the Turkish folks with their ASELSAN KORAL system during the Syrian crisis.
If India gets S-400 after some years, parts of Pakistani airspace will be within its firing range. Since most PAF Airfields are 100-200 km from Indian border, S-400 will become a threat for its aircraft even in Pakistani airspace. Being a land based EW system, can KORAL jam S-400 missile guidance within its 100-150 km range ? And since PAF has less $$$ available, how much will each system cost ?
Pakistan purchased 3 EW systems two years ago. But, the type's name was not reported.
10 if bought off the shelf, still 25 (400 missiles/ main reason is deterrence and real capabilities against a large air force) or more is best, mostly if Pakistan can make them locally through ToT..
With little money in pockets, purchase of even 6 systems is going to be difficult. It will be purchased in batches AFAIK.