I think half of this question can be half answered fairly easily (so this is a quarter of an answer).

People making very long exposures on film needed to hypersensitize their film to deal with reciprocity failure. Those people were almost exclusively astronomers. None of those people will be using film now, and certainly any observatory with the financial means to hypersensitize film will be spending their money on improving their digital sensors instead, so whatever processes and suppliers they had will no longer be supplying either hypersensitized film/plates or the equipment to make them.

So, no, there will be no companies producing hypersensitized film or the equipment to produce it, as the market has entirely vanished. [This is the bit of the answer I am confident in.]

If you wanted hypersensitized film now (presumably because you want to do retro astronomy, like the person who you reference) then the cost of it would be the cost of setting up your own system to hypersensitize film. If you're lucky you might be able to acquire equipment cheaply from observatories which used to do this.

I don't know what it used to cost: I imagine it was never cheap.