Wikipedia itself raises more than $120 million per year. I don't think a telescope could attract as much in donations as Wikipedia, but it is interesting to see how high could donations possibly go.

The only reason Wikipedia can do that is because it's at the top of 50% of all Google search results. Constant epic scale exposure that Wikipedia has been able to use to push for donations (and further to build up a routine of it, an understanding of how Wikipedia operates, to millions of people). Realistically Arecibo has nothing like that to leverage. Donating to Wikipedia is a value to action instant feedback process: you land on a nice and helpful Wikipedia page, you derive value, you give some value back; again, Arecibo can't offer that kind of in the moment, click of a mouse, value-donation gratification to large numbers of donors. Arecibo's donor pool is mostly the Paul Allens of the world.

TLAs have lots of money.

Arecibo was in full operation before the cables broke. If you replace all the cables and hardware and reassemble it shouldn't cost anywhere near $80 million cause you're not starting from scratch.

Assuming the people supplying the operational funding want to continue to do so it shouldn't take more than low millions to get it going again.

It would be way more expensive then that. You can't just inflation adjust.

Construction has a lot more costs these days - have to take care of the environment, not kill your workers...