Somehow I came to understand that the HI and HIX were being used for refugees or something similar. I believe they never reopened to public since COVID.

In any case, I have gone through DUB a few times over the past few years, and I have not seen either of those bookable in that time.

The CP is a nice hotel. I find £123 a palatable rate given its quality, and I have paid in that range before. Those savings you mention are appealing, although I suspect you'd be taking an appreciable step down in comfort. (Of course, sometimes that's still worth it!)