Nah, their cost is fine. If anything, I'd even increase it.
Or lower it, but reduce their power and add an mkII version with faster regeneration speed (or more HP/armour. Or cloaking. Or faster setup speed. Or anything, really.)
In any case, as is, their cost definitely shouldn't be lower; seeing as they present a very unique utility to the fleet, and a force multiplier well worth the 4000K.