As with the airforce, PN needs to think out of the box. They have a distinct need to improve on multiple fronts and streamlime costs. They need to be cost effective without sacrificing capability.
To that end, they should still pursue OHP in the form of Adelaides. Alamghir was acquired by hot transfers so the cost was low. They took it as is. They later added surface attack capabilities. They should do the same with the Adelaides of Australia and get the remaining 3 as is via hot transfer as they retire. (the remaining 3 will likely be retired by 2020/2021 (as Hobart come online). These have 8 cell mk41s. Put them through Genesis upgrade and install smart s mk2 on all 4 ships and get an 8 cell vls system from S. KOREA for Alamghir and equip all 4 ships with 32 K-SAAM, or Sylver A43/A50 and CAMM for all 4 ships. As the Adelaides have their Mk13 arms still, they could load up to 40 Harpoons each and can fire at a rate or 1 every 8 seconds (since pakistan wont have SM-1, Load the launcher out with Harpoons). Equipped with 2 helicopters, towed sonar and 6 torpedo tubes it will be an excellent all around ship class for another 20 years.
Go for 4 Istanbul class frigate with its 16 cell VLS go for same MR-SAM (CAMM or K-SAAM) for 64 SAMs. With 16 AShM capabilities, this could probably be adjusted to equip it with Babur (10 AshM and 4 Babur for example) when necessary.
That gives 8 modern multirole FFGs with decent Anti-air capabilities, with 4 F-22p and 4 Azmat (and supposedly 6 more FACs of Chimese or Turkish design) backimg them. That is a reasonable surface fleet.
Additionally they could add 4 Y-8GX6 To the ASW Aircraft fleet (supplementing P-3Cs and the ATRs being upgraded by Germany). These can carry up to 8 (supposedly) Torpedoes each and likely to be able to fire C802A AShMs. Could even fire Would add tremendously to Antishipping and Antisubmarine capabilities of the entire fleet. So for 4 new 3 used ships amd 4 ASW aircraft, you would tramsform the fleet. If we remember that the Mcinnery cost Pakistan $65M we can assume that the Adelaides will be in that ball park (total $195, lets round it to $200M) and the Istanbuls are supposedly costing $325M/ship and the rough price of Y-8GX6 would be aroumd $60M/plane you are loockimg at $1.75B,add another $100M for upgrades, and refurbishing the the Adelaides/Alamghir and you have a potent navy for under $2 billion. Of course thats without weapons.