@Zel & Ad'A
You're right, the Styx should come down in price. As Ad'A says, 250 pts is the sweet spot for it. However, if you consider the notion of paying a premium for the extra AC in a cruiser chassis then 260 would do, particularly if the Devs range came down. Speaking of which, I really don't think that the cost should go up if the Devs range gets nerfed, particularly if the Styx comes down to even 260 pts.
The range on the Dev has been both its greatest strength and most incongruent feature. It has been a cheap carrier with great reach on its supplementary weaponry. Without it, it's just a cheap carrier.
Consider if the Devs range was dropped and the Styx came down in price, to even just 260 pts (still overpriced, but not nearly so much and we can justify by saying they pay a 'premium' for the extra AC). Then 3 Styx would cost 780 pts. For 760 pts you could buy 4 Devs. 3 x 6 AC = 18 AC. 4 x 4 AC = 16 AC. Ah hah! Now not only does the Styx/Dev comparison net you less survivability than currently (only +33% rather than +50%) but you actually come out worse in the AC totals, rather than parity.
While the 4 Devs would have +33% focusable firepower at 30cm and an extra 67% offside firepower (for a potential +100% total!), the Styx would have the advantage at 45cm (roughly +9WBe or +25%) and clearly dominate at 60cm. In fact, in the 45-60cm range band the Styx combination gains as much firepower over the Dev combination as the latter does in the 30cm band with enemies in both broadsides.
So for 20 pts more this combination gives the advantage in AC and firepower while the Devs give the advantage in survivability and, potentially, in leadership. This last point is only really valid if you're considering squadrons of course, but in which case an extra ship means an extra Ld roll which will increase your average Ld.
If the Styx were 250 pts and the same comparison made it would be 10 pts cheaper than the Dev combination. This seems about right to me given the increase in survivability, leadership and potential firepower of the Devs, but the 'premium' argument comes in and an extra 30 pts for such a difference in roles isn't too much.
@Horizon
I think the Devs WBs are used more often than you'd think. Yes, as a carrier you can sit back at range and support from afar. Much like a Mars or Styx. But also, as a carrier, there is some benefit to shotgunning your AC and you might want to function up close. Much like a Dictator. Of course, in the past the Dev has had the 60cm lances and probably has a preference for sitting back. However, in many of my games I have found my opponents closing with my Devs to engage them at knife fighting range. I've often been glad of those extra 6WBs.
Similarly, in the few occasions that I have played a Styx I have had cause to lament the lack of broadside weaponry. Of course, I like the design of the Styx, it's quite efficient and I would never consider running it in close to the enemy. However it has often been the case that my opponent has managed to close to a point with the Styx that if it had broadside weaponry I could have manoeuvred to take advantage of this. The same has also occurred when playing against them (my Chaos opponent has a greater fondness for them than I).
@LS
Yes, I myself proposed 3 designs, all of them CBs. One of the was a Hecate carrier. This was proposed because I liked the fluff and the name of the ship and because I wanted an alternative to the horrendously overpriced Styx. It was based upon the Dev.
The other 2 designs were both gunships. One was the Cerberus, though my version was much weaker than the current design, and I deliberately overpriced it considerably (195 pts) so that people wouldn't think it beardy and to maybe inspire an argument for a decrease in price or increase in stats. It was originally 30cm range all round, 25cm speed and broadside WBs dropped to str 6.
The other was the Charon, my personal favourite. This was a CB based on a Carnage for +30 pts. However, instead of 2 60cm dorsal lances it was given 6WBs at 60cm instead. Certainly weaker than the 2 lances that a Murder gains to become a Hades but for the same price. I thought there could be no objection based on balance (except perhaps an argument to bring down the cost), but Nate found a fluff objection instead. Oh well.