For the ones I mentioned you'd be looking about 250-300 a night standard rate iirc. There are cheaper deals to be had (for these hotels) through websites, just had a quick check on laterooms and much cheaper there.
What is increasingly common is serviced apartments - which may be cheaper. And I'm on about real quality apartments mate, not trash. Noticed some on laterooms in Beetham tower (the highest residential building in the country) that Mike mentioned - first 23 floors are Hilton hotel, next 26 floors are flats!
Or there is The Edge (which is literally next door to the Lowry), lovely spot that mate, river right in front of the building, nice big bridge taking you over onto Deansgate (right in the centre). Fantastic neighbours (in building other side of the hotel), well one in particular anyway
There's obviously plenty of other choices there too.
If you do fancy an apartment let me know, I've got a very good contact for you.