I would imagine that both Manchester football teams are playing 'at home' that day...
That can't happen, it's either one or the other - and in any case the fixtures for next season won't be released till the summer. Because of the above (they alternate) one of them certainly will, although they may not necessarily play on the Sat - games get moved to the Sun and even the Mon for TV reasons.
So whatever the reason for the high prices it can't be football related. Maybe too early for the special offers of the cheap(er) hotels to kick in?
Well, that's me told... 
Thanks for that, mate, I know very little about football... geuss we should all look at Manchester hotels a bit nearer the time...
Look on booking.com. There are central some pub/rooms for fairly cheap. I have stayed in Black Lion Arena and found it good, I will stay again when I land in Manchester next week.
Try booking.com , Ray. Many hotels are booked already. Honestly a big football match sounds terrifying to me as an American. You here horror stories like if you accidentally wear the color of a rival team you will be beaten by a group of drunken ,angry football fans.
That right there would keep me from going out in Manchester that night. I find the American football fans shouting at an electrical box disturbing enough. Much less people throwing bottles. Sorry if this offends anyone and if this is just a stereotype feel free to correct me.
However I booked a pay later / cancel anytime hotel just to be safe. In the slight chance I can make it.