The 'ship' part can certainly be low-cost, even without a domestic industry.
Basically, you need to construct the hull and superstructure along commercial lines, i.e., as an OPV. The Damen OPVs the PN is getting likely cost about $50 to $60 m per ship (not including sensors and weapons).
These ships are comparatively lower-cost because they're not using design cues for low radar/acoustic/infrared signatures. So, they're fundamentally different from say the Sa'ar 6 or MILGEM, which do incorporate a range of design elements to make them 'stealthy' -- but also much more expensive.
However, the point of a low-cost corvette isn't to hide, actually, it's the opposite. It's meant to be shown in serious numbers, and for that you need to control the cost. The challenge isn't the hull or engines, but the electronics and weapons. This is where the low-end and high-end (e.g., Sa'ar/MILGEM) are fundamentally the same: cost of radars, anti-ship missiles, anti-sub torpedoes, surface-to-air missiles, etc are all identical.
If you don't know what you're doing, you could end up with a ship that lacks the 'stealth' benefits of the high-end corvettes, but only costs marginally less. In other words, you have to figure out a low-cost (but good enough) on-board weapons and sensor package to control the cost, but maintain capability.
The idea that ships can be stealth, as you know, doesn't mean you can't see them on radar, simply shows a smaller radar signature. The stealthiness of a ship has some major components:
1. Emission
2. Cleanliness of the superstructure particularly the radar mast and other communication masts
3. Shape of the ship
4. Materials used (naval steel / aluminum / composites)
Emission
It doesn't matter if your entire ship is as stealthy as an F-22, if you emit, you become the guy in a dark room with a torch. Everyone and their dog can see you.
Emission control is difficult to manage for a ship as it has to scan a giant area with low frequency radar that can be picked off from thousands of kms away.
For our cheap 1000t corvette, we are hoping to use a simple AESA radar and leave out long range detection capability to off platform sensors.
Cleanliness of superstructure
With the large number of radars and antennas, ships provide a giant RCS particularly because the higher the mast and antennas, the far greater the detection by enemy ships and radars.
For our cheap 1000t corvette, a very clean superstructure is possible as we are essentially proposing using a multimode AESA radar that would attempt to replace multiple type of radar and leave out added capabilities to offboard platforms. Again, a very stealthy and financially favorable choice.
If we tie in the radar as a related development to the radar of the JF-17, we may be able to find economies of scale and scope.
Shape of the Ship
RCS reduction is a great deal about shaping. Now, this shaping can be the same for a cheap or an expensive ship, shape has little to do with materials when we are discussing faceted corvette designs.
Materials
Even the US navy cannot afford to make its ships out of composites. Most Western navies use steel for their hulls and aluminum for their superstructure. This is a little more expensive than an all steel structure. There have been some ships designed as all aluminum structures and some smaller ships using composites.
But we can probably all agree either on a steel hull and aluminum superstructure or an all steel ship. Recently I learned how to cast aluminum and make my own backyard alloys using copper, zinc and Silicon. Its surprisingly easy and one can actually source aluminum from waster material like aluminum cans.
Interestingly, many ships and submarines use an alloy which is about 78 percent copper and 12 percent aluminum for their screws. Now, interestingly I am now able to make this metal and cast objects with it in my backyard. Here are some fun things I've found - 90 percent aluminum and 10 percent copper makes a very strong and light alloy.
Anyways I seem to have wandered off a bit. What I am trying to get at is that if we can source the aluminum superstructure from recycled aluminum, that may be a cheap way to go about doing it. Or one could go with an all steel structure. I don't really care much either way. Or one could go to the ship breaking industry in Pakistan and source aluminum or whatever else from old ships.
Bottom line
A light 1000 ton corvette with a clean mast, an AESA radar.
AShMs
A Camcopter type UAV helicopter
9x SAM
CIWS
Hull mounted and towed sonar (sonars have become increasingly more potent and smaller and cheaper in recent years)
armed UUV
You have an anti aircraft, anti surface and anti submarine capability in a small 1000 ton ship right there, with the capability of a destroyer from the 1980s.
