Anyway, my current guess is to:
a) Make the K cost of basic, laser, mlrs, missile, flak, and lightning all the same. Basic has a very low cost for historical reasons mainly; it used to be much weaker but has really been buffed up to be in the neighborhood of the others (it's still weaker overall, but not by much).
Currently, getting all those MK IIs is 12250 K. That's an average of 2042 K (2041.6) each. A base 2000 K for each turret (MK II) seems reasonable here. A base cost of 1750 K for MK II would put all 6 at 10500 K total.
I think that if you are suggesting that a Mk II turret unlock is worth 80% of a Mk II fleetship unlock, I'm going to strongly disagree with you.
Let me say it with pictures: This is what immobility means even within a single system.
The big range circle is the Missile turret. The mid-sized circles are MLRS, and the small ones are Basic turrets. As you can see, in this system with a mere three incoming wormholes, there is very little overlap in turret coverage for the two wide wormholes, even though those are less than 90 degrees apart from the Home Command Station. This means that defend against both wormholes, I'd need to split my turret placement, giving each approach path half my turrets. That also means, giving up 50% firepower on each approach path.
In addition, remember that distance from the wormholes to the Home Command Station in this image is actually rather short (25,000 range or so). Even so, the Basic turrets, as placed here, would be unable to shoot at AI units at the wormhole itself AND be unable to shoot at units that were very close to the Command Station. Moving closer to cover one endpoint means leaving the other even more exposed. Either way, it just shows that turrets, because of their immobility, cannot bring their full firepower to bear even within a single system. It is not at all unusual for my turrets to be in combat for half the time (or less) than the mobile units in a system are.
In summary: Mobility matters a LOT. Strategically, it allows firepower to be brought to bear in more than one system. Tactically, it allows better coverage within a single system. A unit without mobility is not worth anything close to 80% of a mobile ship. I would suggest it is not even worth 40%, for as seen here, the mobile ships can have twice (or more) the engagement time.
e) Given the above, determine what people think is a fair K cost for "a mkI cap" of immobile firepower, and apply that to a) above. There appears to be consensus that 2500K is a good cost for a mkII triangle or bonus fleet ship, so roughly speaking it seems 1250 is a fair price for "a mkI cap" of mobile firepower (I know 1 mkII cap is more than 2 mkI caps in many senses, but it's closer to 2 than 3 in actual practice). The question is how "immobile" and "2x to 3x the hp, 2x to 3x the dps" (which turrets would then have, more or less, compared to triangle ships) affects the value.
Not sure what you are looking for here. Planning on locking out all the turrets (I kid)?
Based on MK II/2 = MK I, MK Is are currently worth about 1021 on average. Isn't that pretty close to MK II combat SS? I think that's fine. The HP/DPS part, I leave that for those with a better sense for those things.
As I said above, and harped on in the other threat, anything over 1,000K for the Mk II unlocks seems excessive to me. Turrets are just not worth more than 50% of a Mk II fleetship.
Mk III turrets have all the same immobility disadvantages, plus they do not get a Mk IV unlock for free. That means they should cost even less than 50% of the Mk III fleetship unlock. 2,000K is 33% of the Mk III fleetship cost, and I'm not sure Mk III turrets are actually worth that much in practice.