Another backup idea would be to add Harpoon/Exocet anti-ship missiles to the fleet, plus the Orions. You don't necessarily have to have 8 tubes for each ships, 4 would do on the OPVs and 2 would be enough on the IPVs. This would cost much less than acquiring an air combat force, with much more range than a larger gun.
Being the most recent, newest and only supersonic trainer/light fighter on the market, Lockheed sees a market to sell over 2,000 of them. The US Congress, refusing to upgrade the expensive to operate Talons, wishes to start acquiring F-50s next year, over 500 are needed to replace the 40 year old Talons. While this order has not been confirmed, its very likely. There are many nations which operate the F-5 Freedom Fighters looking for a cheaper alternative than the F-16. The F-50 appears to be a winner, using the same highly efficient and ready F-18 engine.