I did some renovation work on this thing. They re-used the existing speaker system, we just re-hung it to work better once all the work was done (and improved the DSP). Near as we can tell the demo team nicked one of the cables during tear-down because nine months after everything was back up, building was open and the girls' volleyball team was practicing, frickin' fifteen tons of Turbosounds suddenly plummeted five stories to crash within about 20 feet of a whole bunch of sophomores who would not have survived if it had happened ten minutes earlier. And all that was, near as we can tell from the information that did get out before UW NDA'd the shit out of everyone, was a single cable whose temper had been altered 24 months previously, causing the whole support equation to divide by zero.
The issue isn't a rebuild cost, it's that the way Arecibo is designed you need to be able to lower the receiver in a controlled fashion, repair and potentially replace the gantry towers, replace and re-string all the rigging and then raise it again.
The minute they lost the first cable that all became a lot more expensive because you have a good guess that the rest of them need to be replaced also. And with braided cable the failure progresses from minor to catastrophic with a quickness - lose a strand and the cable is under more stress so you lose more strands so you lose a coil so you lose a cable so you lose the other cables and the whole thing comes down. And of course, the act of lowering the receiver changes the stress/strain relationship in such a way that stable equilibria evaporate into dynamic situations. It sounds as if the consulting engineer determined that there was no safe way to get stuff down in a controlled fashion, which means they're gonna blow the cables and let it crash.
Cables are fuckers, man. Particularly cables in a tropical semi-marine environment that are 60 years old. This is one of those things where if NSF had budgeted for it all along we might not be here but they no doubt ascribed funds in alignment with utility. And it's in Puerto Rico, a place far poorer than most Americans will want to admit.